In OA all hengeyoukai are to be of small size. What would be the best way to allow for bigger hengeyoukai, ie a bear, tiger, panda, wolf? Would you just advance them adding a plus 1 lvl adjustment for each hit die?
I'm pretty sure a a full LA for each hit die is a bit too severe, but if the creature type also provides other abilities better than "normal" heng. get then the HD=LA is not out of line. A leopard for instance gets combat abilities (feat equivalents) and better ability scores, not just >1 HD.
There are ways to balance the benefits so as to reduce the LA, but they are all DM discretion; leopard with no pounce-rake, or fewer HD, or lower ability scores as an example.