If there is a drift during stationary pirouettes you can check if cyclic is perfectly flat when Servos/Subtrim (tuning) is enabled in the software. If configured with Cyclic Leveler, then it has to be good.
If so, it could be (and mostly is) caused by wrong piro optimization settings.
If piro optimization is OK, then you can check if the unit is aligned to each axis.
And last option it could be caused probably by already mentioned WR BEC noise, you should see errors in the log right after a flight.
Or you can just try this:
1. start your transmitter and the BEC
2. move with the sticks for a while (cca 1-2 minutes as if you simulate a flight)
3. then connect the unit to PC and start the software
4. check your Flight log for any errors.
You can see in this video how it should work:
https://www.youtube.com/watch?v=i1yTBg9 ... kiZdA#t=21And this is 450 size heli and very early version of the unit. Today it should work even better.
Tail gain is for 600-size heli mostly around 70% with 1.3x gain multiplier, so final tail gain is around 90-100%.
But this is very individual for each helicopter mechanics.