The default value in rule_values for Character:ItemHealthRegenCap of 15 seemed lower than I remembered it being.
Best source I could find was:
http://samanna.net/gen.info/buffs.shtml
Samanna's Reference Desk AND The Spirit Realm
Worn Effect Caps (table)
Regeneration 35 (more with AAs): Regen AAs stack
Some sites said the cap went up at higher levels but couldn't find any solid numbers on that.