I set all bulkheads about 55" from the rear bulkhead which is 4" behind my back when seated.
Being tall w/ 34"inseam I can put footbraces in and have room to adjust a little more if needed.
The less cockpit volume the better is the rule.
You may want a higher bulkhead storage capacity or maybe you have a tall person you want to fit in it? Kind of a personal decision.
Other NH builders will chime in...hope this helps.