Parmi veder le lagrime, A te o cara, and the dangers of Italian language

I just finished my first week of rehearsals for Rigoletto and today, my day off, is the one real chance I get to do some in depth practice for the Duke, which I am covering, and Arturo in I Puritani, which I will be covering in May.  I take these roles I am covering very seriously for several reasons.  The obvious:  I want to make a good impression on my employers, and I want to be ready if there were some emergency and I had to go on.  But in addition, these roles are some of the most challenging I have ever approached, and I want to learn them right, free of bad habits, so that the next time I am hired to do one of these roles, I will be well prepared for the vocal demands.
As it happens, each of these roles contains an aria that I rank under my "most terrifying" arias.  These are "Parmi veder le lagrime" in Rigoletto, and "A te o cara" in I Puritani.  Parmi is notoriously challenging because it is full of long lines that sit in the passaggio.  Though the range only extends to a B-flat, the high notes all come at the end of long ascending lines through the passaggio.  On top of all of this, the piece needs to be sung in an elegant, gentle manner.  All of these factors combine to make this aria a true test of ones technical prowess.  "A te o cara" similarly sits in a challenging tessitura - the singer must navigate fluidly from D through high A in a manner that is fairly casual, as the A's and G's are merely a part of the legato phrase rather than climactic high points.  I find F-sharp/G-flat to be the most challenging note of the passaggio for me - it is the one pitch that doesn't know exactly where it wants to be.  In my voice it feels too low to really try to cover it the way I would on higher notes, but it certainly feels too high to be singing wide open.  But I don't like to think of "covering" as a major event, it's just a natural acoustical shift that happens when you are not allowing the larynx to rise as the pitch rises.  Anyhow, Parmi begins on a G-flat, and A te o cara frequently sits on F-sharps.  A te o cara also has a big climactic high C-sharp.  The combination of singing long lines around F-sharp and A, and then ascending to a high C-sharp, makes for an incredibly risky aria. 
I was practicing these pieces today and I found that in both of them, I tended to get mushy in the language because of the long sustained lines, and as the language became mushy, the control and support would also become lax, and then I would start struggling, and I'd get the fast-vibrato syndrome....  None of these things are pleasant.  So I took a stop back.  One general thing that was helpful was to just sing more connected to the body - regardless of the gentle esthetic of the music.  For me this means being aware of the full column of the torso beneath the vocal tract, and feeling a sense of strength in the lower back and thighs.  I also find it oddly helpful, when playing my pitches on the piano, to play them at the actual pitch that I sing them (that is, an octave lower than they appear on the page).  Music for tenors is written in treble clef, but the pitches we sing are actually an octave below what is written.  Now, a coach of mine once told Brendon (the love of my life, and my pianist) that he should always play tenors' pitches up the octave because it will help them to sing brighter or in a higher placement or something.  I find the opposite.  Playing them down the octave encourages the singer to connect to the voice in a deeper, richer way, and in encourages the singer not to reach for the high notes, since they don't sound high.  But apart from staying connected and grounded in my body, I also felt that the language itself was playing a significant role in my discomfort.  I know everyone says Italian is the singing language, and that it's the easiest to sing in - but I find it so much easier to sing in English and German.  English and German have a deliberate feel.  There are plenty of consonants, and the vowels are open and bright.  I realize that my comfort with these languages has to do with the fact that I am American, so the vocal production of American English comes naturally to me.  I was trying to isolate what I was doing differently in Italian - why did I feel like my tongue wanted to pull down in Italian?  Why did I have trouble forming the pure vowels?  I took some inspiration from this video of Madonna at a vocal coaching: https://www.youtube.com/watch?v=cY9GR_-eXHE

There is one point where her coach is helping her with the word "change" which she has to scream in performance.  In the coaching, she is using a supported "shout."  I tried this with the same words she used.  Then I switched to an Italian line to do the same thing - just sort of shout-calling - and I noticed something odd.  When I shouted in colloquial English, there was a sense of stability and symmetry in my laryngeal position.  When I switched to Italian, however, I would feel the larynx slightly move to one side.  I analyzed further and found that this was in response to my tongue moving to one side, because when I formed Italian consonants like [l] or [r] with the tip of my tongue, I was putting the tip of my tongue over to the left side.  Why? Because I associated a particular fluid sound with the Italian language, and I would subconsciously change my voice and my formation of consonants in order to create that sort of a liquid sound.  I tried to deliberately create an Italian flipped [l] while keeping the tongue stable, symmetrical centered and forward, and the result was instantaneous - I was forced to put real support behind the consonant, and with this came the feeling of my real, direct voice, rather than the mushy faux-Italian thing I was doing.

I should mention one more epiphany, particularly in regards to the "A te o cara" high C-sharp.  I had this epiphany a year ago when trying to work on legato singing.  the phrase in the aria is "se ramme---enta" going from an F-sharp to an E, and then ascending on the middle vowel of "rammenta" to the C-sharp.  This is a large leap, and it is tempting to try to do some kind of big switch.  Some tenors do so successfully: https://www.youtube.com/watch?v=8Bh7snchrq0
Here, Gedda aspirates the high note, as though it has an "h" behind it.  He does so to great effect, and produces a beautiful C-sharp.  I have found myself less successful with this type of approach.  My epiphany was continuing the breath entirely legato through the ascent, as though I were just continuing to sustain the F-sharp.  This involved a sense of constantly moving forward through the breath.  The feeling as I did this was that it was not possible - surely if I didn't reset in some way, I would just top out and wouldn't make it.  But to my surprise, I ascended cleanly and robustly to the high note with no problems!  After forgetting about this a little bit, and having some trouble with that particular note, I went back today to the idea of really continuing in a true legate through to the high note - and once again, this approach was met with consistent success!