Of my 10 kilts, most hit around the top 1/4 of the kneecap. My Gray Stewart, I made longer, it sits in the bottom 1/4 of the kneecap. The Lindsay tartan, which I throw in these days, sits above the top of the knee, just barely. My X-Kilt is at the bottom of the knee and my digital camouflage reverse kinguisse hiking kilt is at the top 1/4 of the kneecap.

Upshot? IMHO, wear it where you like it...anywhere around the knee is fine. Showing 3 inches of thigh might be grand, but IMHO it's not very kiltlike. Wearing something that ends at mid-calf is also grand, again IMHO, not very kiltlike.....which doesn't mean you can't do it, of course.