I'd guess the issue boils down to density, and thickness.

You can try purchasing some replacement foam, perhaps laminating a thin (maybe .5") piece of low density material on top of denser base material. Going with material that's too low-density will mean bottoming out to the plywood - especially when having some fun :)

The other option would be to use thicker material to start with. IIRC my old bay-window westy had thicker stuff up there and with the design of the hinges you could get at least another .5-1". I'd imagine that ventilation might be an issue, but you can try.

I recently priced out replacement foam from one of the online sites and can dig up the URL if anyone's interested.

john