How does auto-tune determine atc_accel?

I’ve got a couple small ‘racer’ style copters. Auto-Tune in 3.4 sets the atc_accel level much lower than it was doing in 3.3… The copters fly very smoothly and well after auto-tuning, but they’re sluggish.

w/ 3.4 they’re in the “slow” area (if you look at the full parameter list, it gives you ranges for slow, meduium, and fast response.). W/ 3.3 they were in the “fast” area.
Can I simply increase them to the fast range w/out affecting the tuning too much?

I’m wondering how it determines what to use for that value?