My break has gone up almost 2 wholetones, but I think it is more due to adapting to having proper resonance at all times- because my voice sounds weird otherwise... It sounds like I am a girl trying to imitate a guy voice so I don't ever drop my larynx. This is purely due to habit, and it is probably correspondingly strengthening the muscles associated with using a feminized larynx position further cementing it.
Someone who has successfully feminized their voice without surgery would likely find the same exact thing about getting used to a new larynx position and how that changes the break of your voice. The only exception being that it is possible to retrain a non-VFS'd voice to use the lower range again. After VFS, that possibility is permanently eliminated.
And yes the lip flutter exercises and sirens have definitely helped I think. Yeson has you do voice strengthening exercises and those are the main component.
This is what I do twice a day (as directed by Yeson, until I am 12 months post op), but anyone could do this to develop their voice regardless if they've had the surgery:
warm up
• soft lip trill on F3 (this is towards the bottom of my range and feels like somewhat of a low note)
• soft "neeeeee" sound on F3
• soft lip trill on F3
• soft "neeeeee" sound on F3
stretching & contracting (stay quiet, careful not to strain)
• soft lip trill siren from lowest to highest x 4
• soft "noooh" sound from lowest to highest x 4 (using air like blowing a candle)
(current range D3 147hz to Ab5 831hz)
power
• hold lip trill on C4 as long as possible (relax and breathe from diaphragm)
• hold "noooh" on C4 as long as possible
• hold lip trill on D4 as long as possible
• hold "noooh" on D4 as long as possible
• hold lip trill on E4 as long as possible
• hold "noooh" on E4 as long as possible
• hold lip trill on F4 as long as possible
• hold "noooh" on F4 as long as possible
• hold lip trill on G4 as long as possible
• hold "noooh" on G4 as long as possible
warm down (quietly)
• G4 down to G3 siren using "nnngg" sound, like in the word "sing"
• G4 down to G3 siren using "nnngg"
• G4 down to G3 siren using "nnngg"
• G4 down to G3 siren using "nnngg"
It's a really great exercise while driving alone