I’m wondering what’s the typical amount of PMMA used when you go for the touch-ups. Also, do you scratch some gains from touch-ups (0.1”-0.2”)? Is this something you can expect, or just the aesthetic correction?
It depends but you're often looking at 5cc-10cc's. If it's just some smoothing out, look for it toward the lower end. What often happens is a patient will usually hope for "a tad more Girth in addition to touch up" hence why you see some reports closer to the 10cc side.
Touch-ups in it of themselves aren't designed for gains, but small incremental gains are sometimes inevitable in the process. Touch-ups are meant to provide a more natural end-result, especially since dermal fillers aren't 100% predictable on a first round.