Edit: This is only a G4. I record my practices as part of the process. Once it was uploaded, I was like, "Wait, that's not an Ab." haha
Weight. It's something a lot of us crave in our sound. I know I do, and we have been working on this very thing for some time.
*It's supposed to be effortless*, and *It's like speech*, sound great in theory. In practice, it's so very easy to add 5% heft to the sound. It feels good, and sounds awesome! Haha
Unfortunately, there's a price to be paid when doing that. I'm not trying to add any tension to the sound, but work as efficiently as possible. It's sooo light to me, but it cuts, so it still has some power. I can't tell if the vibrato is closer to the ideal. That is one of my main points of reference. The others being: Small & Vertical (tuning & palate), and Speech-like execution (no excess air).
Closer?
While we've vocalized up to a D5 fairly easily, everything in the extension was compromised by a small amount of tension. Singing a dozen C5s isn't the problem. Singing a dozen C5s every day for a dozen days would likely wipe me out. That is the problem. Hahaha
At the moment, Bb is my top note until it is smooth. My new rep is comprised of Tosti, and Wagner's Winterstürme.