I had issues with rudder input on aggressive collective use. Still do, but it is getting better. Only way to train it out is to be aware of it and perform maneuvers that force the problem to come out so you can develop muscle memory in the correct way to do it.
You said that you don't have the issue sitting, but do when standing. This may indicate that you need to move your Tx neck strap, if you use one. Otherwise you may need to find a different level to hold the Tx at or perhaps a new angle. Before training it out, try different Tx positions and angles to see if you can find something that is comfortable and reduces or eliminates the issue. If you do use a neck strap when flying IRL, then use it on the sim too.
