I suspect that 101.6 gets rounded to 102, since this is what I get
If I use numbers under 100 so they don’t get rounded, it seems to work properly.
As for your issue with measurements in inches, that’s because each increment is .1mm or .004 inches, which is smaller than the accuracy of the indicator. And since it’s the same exact slider with the same exact values as when the game is set in millimeters, you will often not be able to get exactly to the measurement you want.
Here is how close I could get with the first set of numbers you gave:
4 inches gives you 101.6 millimeters, which is possible with the slider in millimeters, however 3.75 inches gives you 95.25 millimeters, so you have to use 95.2 or 95.3.