Just a couple of comments: On a man, the waist is almost always at the naval. On a woman it is somewhat lower. This is pretty much a constant, with only very slight variations. (Don't ask my why, ask the designer!

In the Navy we used to have a joke about a pregnant woman and a 20 year Chief (Petty Officer, MSGT to you Army types) having the same figure problem.

If the kilt is made to fit you, then these measurements are critical. Since all the off the peg kilts are too short for me, I cannot say where the best place to wear them is, my guess is where they feel comfortable.

I agree it is easier to shorten a kilt than to lengthen one, at least until they get a Kilt Stretcher. So just wear it wherever it is comfortable. Just remember not to have the length below the middle of the kneecap. That just looks sloppy in my book.