Well, I hope that this fix is not my isolated case only. Someone should try it to confirm if it helps to get uniform mesh tightness 360 degrees around. My "shims" are just folded sticky note :D Different shim thickness will have different results.
Mounts: ES EXOS-2 PMC-Eight, SW AZ GOTO
Scopes: SW 200P, SW 130P
Cameras: Canon T3i, Canon XS, SV305 Pro - IMX290