Gem Studded Cost reduction not working On Flame Breath

Specifically the cost reduction does nothing for rage cost with gem studded. I tested numerous times with many different configurations. I can immediately tell a very large difference if i run efficiency 1 which should be the same value. But zero value in any configuration of weapon sets (1/2/both). With all supports pulled off and testing 1 at a time etc.

Gem studded has identical wording "skills have x% less cost) to the efficiency support gems so I'm not sure why this isn't working. In looking, I noticed it does work for the mana cost, but not the rage cost per second. Kinda killing the vibe on my flame breath build.

As far as I can tell the other two benefits work fine.