Some builders angle the rear bulkhead to reduce the volume in the cockpit just behind the seat. I don't as I prefer that spot for my paddle float or camp seat.
I always go vertical on the front. The only reason to angle would be for your foot angle if you don't like foot pegs and push off the bulkhead. Bad idea IMO as you can easily cut foam angled and preserve the fit options for your boat.
I like the forward pulled back as much as possible to allow footpeg adjustment for tall people. Keep vertical=keep simple