It isn't just the volume injected, it's how your body responds to the presence of the microspheres in terms of how much collagen is produced. My first ever
PMMA injection was done in like 14-ish years ago using a 20%
PMMA of what I believe was 15cc's (memory a bit stretched here, but don't believe it exceeded 20cc's for sure) -- I gained a whole
Inch in
Erect circumference. That was very a very above-average gain. Somehow my 2nd appointment (with less volume) didn't seem to yield nearly what I expected it to based on whatever
"mathing" I had in my head.
This is why many injectable
Phalloplasty practitioners will often quote a 0.5-0.75" gain as a
"typical but not guaranteed" result after your first go. Think about how your hair or nails grow faster/slower or thicker/thinner than other people you know (while not collagen, I'm using the example as a comparison) . Some people recover faster than others from wounds. It seems like physiological processes, while identical in terms of execution, can vary in terms of duration and/or degree.
The size range that you can gain, which I quoted above, is based on average ranges reported by both Clinics and their patients on the first go-around.