Search deeper here or in the DIY Forum. The founder of Kick Ass Quilts sewed up a set of down-filled pads for an NX250. (ISTR that four of the pockets are the same size, and just two of them smaller). Yes, the pockets are pleated, so the have a height of about 2". IIRC, the owner, who wrote the specs for the job wished he had made the pillows / pads a little larger.
Bradley in this Forum also made his own pads and a video of them.
Clark surely tried to size the pads of the Z liner optimally. But, then again they seem to have stopped with just one layer of 5oz Climashield. More would have been very bulky, and not many camp in the cold of winter.
A serious DIY effort would start too big, and with pins, and then cut down insulation and re-pin to fit before the final sewing.