You're using it as a sandwich plate, the more important thing is that you grab enough surface area on the firewall. The aluminum plate isn't going to be the part that deforms, the weak link is the firewall.
I agree - you want to bear on as much of the firewall as possible to distribute the load. Space is really limited on the inside. I can see a little bit of firewall deflection on my Cuda but it is pretty small.
