I don't know what the experts will say, but I think there are several factors involved in the "swish" factor, pleat depth being only one of them. Pleat depth combined with pleat show yielding the number of pleats over a specific kilt edge distance (pleats per foot and yards of fabric per foot of the pleated section), combined with the weight of the fabric, and the over all length of the pleated portion of the kilt below the fell. The combination of the overall number and depth of pleats with the weight of fabric and length of the pleats IMHO is what gives it is overall movement, which is pretty much directly related to how much pleated yardage their is and how heavy and long that part of the kilt is. Probably the reason the military kilts have reportedly been going up in numbers of yards involved in their build ups over the last 150 years of so from 4-5 yards to 6 yards to 7-8 yards---the improved "look" in motion during parade in particular, since it is pretty obvious that the kilt has become less of a piece of attire fit for modern warfare than it may have been percieved to be a couple hundred years ago.

Kilt makers and historians please chime in.

jeff