This sounds more like interaction in the head that you should not have to mix out.. I would check your timing on the head and make sure your anti-rotation block is not out of time... a few degrees forward or back can cause interactions like that. You should be able to fix it there and then remove the offending pmixes that your are talking about.. I would never put mixes like that in there.. there are other things you should look at and make sure if flys were you want it to..
Also check you balance at the flybar and make sure your not nose or tail heavy..