Yes...it can be frustrating...for me...most days all I make are pressed beads so you think I'd be able to do it with my eyes closed but sometimes that's just how it goes. You have on days and off days. I've made so many pressed beads now that I can well gauge how the bead is going to turn out but I still refer back to my original playdoh samples for sizing.
It took me a lot of time before I was getting consistent results especially since I wasn't making plain beads but ones with added design on top of the core which can totally throw off your base bead sizing.
I think in the end it comes down to muscle memory...the more you do it the more familiar it becomes and pretty soon you don't even think about how much glass you're winding on. Keep at it. You'll get the hang of it
/Yee