Coff:
I believe there's a minimum "compressibility factor" for the seat cushion, in this country at least. The gent who restored my Chipmunk was adamant about getting this right (and quite scathing of the "soft" seat cushions that had been in VH-RWI), so I ended up with quite firm seats. Not that I'm complaining, I believe the RWI front-seater is permanently wheelchair bound now.
D9