wedge backrest size

[gscmarine]

Hi all,
   I am putting an estimate together for a a big benchseat on an outdoor deck and the architect has drawn out the backrests to to be wedge shaped.this is no problem as I have done them before and can get the foam cut to shape.My question is what would be the most comfortable shape ergonomically (i.e.  3 inch wide top x 6 inch wide bottom?)It's been about 8 years since I have done one and can't remember what size I used.Thanks in advance.
Geoff

[kodydog]

I'm sure the architect has an idea in mind how the cushion should look. I would pin him down on this if you don't want to redo it. Ask about form follows function and the rule of threes. That should blow his mind.