Sorry to bump an “old” post, but this was revived in the last couple days, and has a BUUUNCH of information.
The (?) part is incorrect. I did some playtesting to test this earlier today, I got a good Sprint speed item, but has a -Heal Power attribute to it, and I wanted to see if it would gimp Rath’s play at all. I was Lifestealing with a base Melee for 12 HP. I had a +10% Heal Power item and a +10% Healing Received item. With a base heal of 12 HP I should’ve seen at least a 1 HP increase with each item. I activated them one at a time for testing’s sake and each time my Lifesteal remained at 12 HP. I saved video, but have yet to upload it anywhere.
From what I can tell upgrading it does not increase the rate of health regained (need to do more testing to give precise amounts on that as well), but there seems to be a +Damage Reduction buff as long as the Healing buff is active.
I was supposed to be testing this while I was testing the other stuff I was working on, but I forgot. I am pretty sure they work just like Crystal Shard Clusters (two minutes after killing/summoning them).
I am still curious as to what minions exactly are considered minor vs major.