The absorption coefficient of foam is gonna be determined generally by the thickness and density of the material. I don't think the shape has much to do with it other than it a) affects the thickness of the material, b) provides more surface area in the same amount of space and c) might provide *some* limited diffusion at very high frequencies.
With all that said, foam is way overpriced and does damn near NOTHIN in the the lows where you really need it. So skip the foam altogether and stick with what works- rigid fiberglass or rockwool (damn, I feel like a broken record sometimes)