XY First layer Compensation is doubling the requested offset causing gap in shell when thin walls are used

[gpread]

2.3.57.0

Creality CR-10V3 (modified), Marlin 2.0.8.2
Windows 10 - 20H2 (19402.1165)

Compared to prusaSlicer , SuperSlicer is applying twice the amount of compensation, e.g. with a setting of -0.2 mm its adjusting each edge by 0.4mm.

In my case with a single layer base to a custom support with 0.4mm nozzle and thin walls, this results in a gap (as the first layer has been shrunk by an entire perimeter.

I believe this also can/is causing first layer perimeters to at times be unreasonably identified as overhang perimeters too (I noticed before but at the time didn't identify that this was because the applied compensation was larger than expected.

With XY First layer compensation set to zero (default)

With XY First layer compensation set to -0.2mm

1. Load the project file (attached below)
2. Make sure Print Settings->Slicing->Modifying Slices->XY First Layer Compensation->First Layer is set to 0mm
3. Slice the model, then examine the Width view and note that the base of the model and the thin wall above are connected (no platter visible through the model)
4. Go to Print Settings->Slicing->Modifying Slices->XY First Layer Compensation->First Layer and set it to -0.2mm (which is ~half the perimeter and thin wall width being used)
5. Re-slice the model, then examine the width view and note that the base is now detached from the thin wall above

In order to see the same results as with prusaSlicer the value used needs to be halved (so in this case -0.1mm).

[gpread]

XY 1st layer Compensation is 2x the requested offset_SS_Issue#1547.zip