Yes I know this can be difficult. The non Traditional Helicopter Parameters (ones with out H_) are likely the multicopter defaults which in many cases don’t work well with the helicopters. So in looking at the param file you posted on the other discussion thread, I see that your setting for PIDs in Pitch and Roll appear to be in line with Chris has shown to work. The IMAX parameter is not the one you want to change for what you are seeing. It is already at its maximum so it will allow the integrator to provide as much input as it needs to hold trim attitude. But it doesn’t sound like holding trim attitude is your issue but that you are oscillations due to disturbances. I’m not sure if this is a feedback thing or just the aircraft not able to resist disturbances. Since your P values are very low, I suspect it is not caused by them. It could be your D value in pitch. You might try setting that to zero and see if this issue is still occurring. If it goes away then it could have been a feedback instability caused by the D gain which only became an issue in FFF. You could also try raising your I gain a little more but I’m not sure that this will help.
So another option might be raising your P gains to determine if and at what value you see oscillations start in a hover. I think if you could raise these a little more, it would go a long way to helping reject wind disturbances. But once you see the oscillations, you will want to back off by at least 0.01 and make sure you can’t excite them by making sharp inputs. Then you can build up in forward flight speed and verify that you aren’t seeing any oscillations. If you raise the P gain, then you may want to lower the VFF by the same amount as you might feel the aircraft is too responsive to your inputs.
Hopefully this helps.