You're within acceptable heights. If it were me, I'd take into consideration the slop in the hitch a riser would add. We have a 4" riser and it was terrible. I added 2 hitch immobilizers to snug it all together. I wish we didn't have the riser.
IMHO if I were within the limits I'd leave mine alone. The more you add to the hookup your just adding more things to go wrong.