This is a pretty simple change imo.

Behest I 3-13
Behest II 13-23
Behest III 23-33
Behest IV 33-43
Behest V 43-50 (yes you need to add a new behest set in for R43+

Very simple and easy restrictions. That make sense. 3, 13, 23, 33, 43 is when you you get access to leves at higher tiered camps and 10 ranks later new camps open up. So restrict it in line with the way the leve system works.