As I understand it the third formant is a possibility to make a decision about the sound of a voice. I dont think it is as important as one may think. Of course, if you are in a better range there, the overall impression will most likely be better. I cannot yet tell you what the surgery changes in that respect - but I suspect it has an effect. What is most apparent for me at this stage is that the timbre has changes, the low undertones are gone. I still have to improve my resonance and some things about the way I speak and intonations - but I think I am mostly there in those, I just have to let go and relax more , now that my voice has changed and doe snot need to be forced anymore 🙂 - voice therapy, as people tell here over and over again is needed in conjunction woth the Yeson procedure. Its a voice supporting surgery - it makes it easier and more relaxed to use the voice in a feminine way and it eleiminates some male traits. What you do from that stage on still is up to you and voice training, therapy, rehabilitation,...