For me, to get the 100Micron x/y (192mm x 108mm) calibration grid to actually land on the bottom of the build plate it requires I add “Shims” in an effort to tilt the projector BUT the key-stoning effect is so pronounced (corners are no longer square) I didn’t think it was a good idea as I suspect the focus will be way out of whack.
I opted to zoom in and have a hint of space between the edges of the build plate and the printing area/calibration grid (which gave me a print area of (184mm x 103.5mm).