First, thank for responding.

I have a 4 yard strip of fabric.

After marking the minimum width of the apron and under apron I put in the provisional 'nips' in order to form box fronts and folds, starting from the centre back join. (I round the size of pleats down to gain enough fabric for under apron pleats.)

This is the best aproximation in type I can make of the folds, seen edge on.

Inside of kilt
From the centre back ./_\/_\/_\ towards the under apron.
Outside of kilt.

The fabric is nipped together at the base of the Vs, with the _ being a single layer of fabric 3in wide, the box fronts, and the Vs are double and about 2.5inches high, being the 10 inches of fabric in the two 'wings'.

The result gives me five layers of fabric behind most of the back of the kilt - I chose a box width of 3 inches and each fold was 10 inches which is flattened into two 'wings' one each side of the 'nip' (which is just a few stitches at the waistband level to hold the provisional design)

Those wings overlap. They will have to, I think, if I am going to use the whole 4 yards.

When I put in the flare to the hip during the actual construction of my take on this design of kilt the amount of overlap will reduce but there will still be 5 layers in the centre of each box.

If I make the boxes so that the wing folds are half the front of the box, which gives me three layers of fabric all along the waistline, when I flare for the hip there will be areas of single fabric.

Using a 'no more than three layers of fabric' method it will use even less fabric for the back kilt than my original thought on this method, as each yard of fabric will become one foot of box pleating.

Have I made an eroneous asumption or design error?

Does the normal method just use less fabric than I assumed? ??:

Pleater