I, too, am badly in need of an advanced toggle to adjust the overexposure height. At least I think I am. I’ve got a finished, direct-on-base part that comes out beautifully except for a terrible, ugly-arse layer line near the 5mm mark.
I spent hours troubleshooting layer shifting, manually constructing loads of supports around that layer, etc., before I examined it more closely and realized this may not be a shift, but rather something more like overexposure or compression. To the touch, the walls feel like they contract inward around the entire perimeter of my print after it hits that layer. Smells like an artifact of overexposure switching off.
When it occurs, the line is always consistently at the same height in every print (roughly 4.6mm; also note my model has 0.45mm of “extra base” at the bottom which gets consumed by compression).
Interestingly, in one test where I sliced my model at 6.5mm, the line did not occur (picture on left, notice the clean space under the “e” and rest of text). Does Preform have some logic in it that adjusts overexposure based on model geometry?
I do also get some banding at layers where the holes are encountered but it’s less pronounced.