The “rotated guider on a GEM” requires that everything (everything) be set up right. The procedure is complex, time consuming, and at times irritating. But once done, it becomes automatic hands off all angles on both flip states.

The main thing you absolutely must have before starting is an accurate field-of-view indicator. You need it for routine observing, but you also need it for setup. There is a load of info in ACP Help about this and how to do it the easy way (not hunting for guide stars and getting the wrong one, or trying to get your camera in at 0 mechanical angle or rotating from TheSky and calculating the offsets, etc. etc. You can driver yourself crazy.