@GuyK, also set the calculation tolerance as small as you are able
.0003mm is the smallest tolerance I can enter with MC9 (I work in inches and .0001" is the smallest calculation tolerance I can use, so in metric you have finer tolerance).
I have posted
On the old grzforum I once likened MeshCam’s toolpath calculation to a blind person using a cane to navigate. If the cane tip was too big relative to an opening, the person couldn’t tell the opening was there at all. That is having the tool being too large relative to the opening. But tightening the calculation tolerance . . . is a major factor.
This won’t magically let you make holes the same size as the cutter, but will give you the best conditions. As @WillAdams said, my rule of thumb is cutter about 90% of the smallest hole/opening.