IIRC, the front flip up sight comes in more than one height option. One will work with the rear diopter. The rear diopter's are calibrated for different barrel lengths. The 10" has it's own and the 14.5/16" has it's own. Marked with "." or ".." respectively under the "2" setting.
ETA: the 28mm front should work with the diopter; the 33mm front is meant to work with the folding rear.
If I may say so, even if you get the right combo, this sight selection sucks for practical use. The folding front does not afford you the same sight picture as the fixed front and is more challenging to use. It's too small and the pin clip can come off easily...doesn't help that it's sitting on the hottest, dirtiest part of the gun (especially on the 14.5 if folded). Several do not take the time to properly zero the diopter drum, and even when they do, we get countless questions regarding "co-witness" of which you have relatively few good options.