So 1A basically told you that in Fixed Mount, it won't drift. With no Heading Assist, it will drift a little. I know they have worked together with the engineers at Freefly to get their product to work and to improve the stability of the interface. Reading back, are you using a Movi Pro or M15? This is a thread in the Movi Pro section of the Forum, so I assumed you were discussing the Pro, but if you're using the M15, then the Mimic you're using is the Mimic Beta, which is different than the Mimic Pro. Both of them have issues with drifting that has been discussed at length here, but I think it's important to say there's a difference between Mimic Beta and Mimic Pro. Solutions for drifting in one system may be different than the other.