There is a thickness difference of ~0.25mm between the upper left corner and the center, not ~0.01mm; my measurements are significantly outside the +/-0.06mm tolerances claimed on the measurement sheet. Also, my measurements are very consistent across prints, which makes me hopeful that if I can actually make adjustments, I can achieve better accuracy.
In any case, my primary concern--as expressed in the title--is that even dramatic changes to the printer settings seem to make no difference in the calibration print. To me this indicates a problem, regardless of how acceptable my current measurements may or may not be. Could somebody please comment on this issue?
Thanks for the advice on adjusting the model's geometry. I may need to resort to this, but I am trying to avoid it.