Man, brutal. so one of the main things that affect a throttle curve is the idle adjustment slider. Is yours in the middle or up/down? It really affects the curve at the low end.
I took the new revised quad out today, same drift so i fixed it how i had it fixed before, subtrims looking first at the green sliders in assistant, then fine tuned it in the sky. If you look when your done calibrating, do your green sliders sit perfectly centered? I think mine moved the ail 2, ele 3 and rudder 1.
This is interesting, one thing i notice when calibrating is my throttle slider when the stick is at 50 dead nutts in the middle, the slider is way off from center and green, it's a few ticks over center and black