Thread:Cat2006house/@comment-25771421-20160715144236/@comment-11218751-20160715182948

You are correct. I did some research on this and learned that the interaction between and  or  is additive. To put that into perspective, only and  affect heal in the manner of multiplication. They are the effects that amplify heals after the addition of all bonus healing effects is involved.

Thanks to Riot Xypherous and Kayle Bot at Reddit, an infographic has been complied to illustrate the interactions among all of the major direct healing buffs:

(Source)