@goldensnake, here are my test results, which confirm your findings.
First picture: 1 layer thick with Z-offset=0.1mm and Layer_0=0.25mm, 1st-layer-print-speed = 25mm/s, FS v0.82 and Cura2, no height adjustment tape. Layer was damaged while taking off glass platform, however next to the coin, by the torn hole, is thinner than the rest of the wafer. Still, the result is acceptable by my standard since I don't print 1 layer structures.
Picture 2 below: Added 2 layers of Scotch tape on opposite side of the coin where the print was thinner. Print settings are the same but raising the opposite side made the coin side even thinner. Notice: I forgot to add more glue stick in between printing, and one side shows poor adhesion.
Picture 3 below: Similar to Pict #1, no tape adjustment, same Print settings, but changed to Cura engine (I changed to Cura as I am more comfortable with it), also left the print on the plate to avoid damage. Print shows thin quadrant right of the coin (black glass showing from underneath). As Pict #1, result is uneven but acceptable for 1 layer. The reason
Picture 4 below: Same Print settings, Cura engine + 2-layer Scotch tape adjustment. Most uniform print so far for a 1-layer wafer.
Conclusion: I am not an expert but I think most probably Flux Calibration does not create a height correction mesh (matrix) or maybe it needs more data points to compensate for platform slope from edge to edge.
I would also like to add that, even without the tape adjustments, I find my printer very reliable and perfect for my needs since I don't print single layer structures (they are also a nightmare to lift from the printer). By the 2nd and 3rd layers almost all imperfection disappears in general. However, it would be interesting if @proclaim or someone from Flux could comment on the Calibration method and the leveling issue.