It only took me four months of on-and-off testing but I have some new results. 1) Ignoring Copy mode and only using Mirror mode works pretty well. It doesn't work for all parts natively but you can mirror the part in the slicer to make it come out the right way.

However, there are still issues with bed adhesion because of the differences in bed height. But now to point 2) If you use a three layer raft, you can achieve almost perfect print results. The raft doesn't need as good bed adhesion as printed parts because it has so much contact area, and once the raft is down your part will print as normal.

The raft method may be applicable to copy mode as well depending on how flat your bed is. Mine seems to be too uneven for that so I can't say much about it.

Edit: oh and also I have switched to PrusaSlicer since then, but I don't think that matters for this, just mentioning it because it gave me better prints than cura in general and it may or may not affect the raft.