When I had only one 9 yd wool kilt which was not bespoke (for me) I wore it very high ('cause it was way long over my knees otherwise). My second 9 yd wool kilt was made bespoke for me and I wear it comfortably about 1.5 to 2 inches above my navel which makes the drop fall at just above the middle of my knees. I subsequently got my other kilt altered to the same measurements. But -- where one's navel is and where one's "natural waist" is are not necessarily the same. I find that wearing the kilt so the top edge is just slightly above the midway point between the top of my hip and lower ribs is most comfortable, and evidently looks good too (or so I am told).
As Jock has already said, the key point is where it falls at the knee, adjusting the top up or down to make sure it is "knee perfect!"