Flesh and stone reducing self damage in sand stance

I have a build that depends on exact numbers of self damage taken via forbidden rite. I can consistently adjust that damage using flesh and stone's sand stance, taking 19% less damage, and messing up my triggers.

Expectation: Flesh and stone sand stance only applies to enemies, as per gem description.

Bumping this, I have a sneaking suspicion this probably applies to heartbound loop and trauma from boneshatter too. Doing some independent testing now.

E: As far as I can tell, it looks like it works vs boneshatter too. Some crazy variance and of course armor and physical damage calcs make it hard to 100% tell what the difference is.

Can confirm it's definitely affecting heartbound loop damage.