Angling the aft bulkhead is merely to reduce water volume in the cockpit by more or less following the curve of your rump. I have also seen vertical curved bulkheads that rap around the hips to reduce cockpit volume. I do not see the effort is worth the quart of water that is excluded from the cockpit. More importantly, locating the bulkhead right at the rear of the cockpit cutout makes dumping out water quick and complete.

The front bulkhead is tilted when used as a footrest in an effort to make your ankles more comfortable. Locating the front bulkhead close to your feet will reduce a worthwhile volume since most designs and kit design for very long legs.