I just tested for you, i dont know if it is intentional or a bug but only Scalp(Any offhand special skill) heals from Prayer, and Toss(any offhand main skill) does not heal from Prayer.
And according to the Patch Notes, only prayer healing off of % of base hp was mentioned:
So you can maybe write a bug report or wait for a dev or mod to reply?
EDIT: Now that I think of it, it does indeed make sense, spamming offhand main skill, is stupidly OP and broken…And plus the OH Special skill has an incredibly low cooldown and still heals prettily OP high , i remember mine healed like 39k, now it heals 26k(still pretty high if you asked me), I can still tank a huge pack size w/o any hp per hit or hp regen and without moving at all.