I have just two Icons, one to Ti(i) and one to Humbaba - Tii gives 400+ XP, Humbaba ~180. Tii gives 120 energy, Humbaba 200. I've had Humbaba a little longer and have tithed more to it.
Any ideas what the values depend on? Maybe their global favor? Or the favor I have with them? (I imagine I'm doing better with Humbaba in terms of current favor, but I haven't checked.)