I am sure this has been discussed somewhere, it seems to be hiding on me, but what is the best Ghost level to hunt vs the energy/rune drops if all things are equal?

I have read, and believe, that unless trying for Gems only found on an Uber that level 5 Invaders are the best for materials/energy. It seems sad and bath math on the game's part for this to be the case. I just would like to know if the same is true for Ghosts.

Ghost and Invaders at higher levels seem to be more focused to gaining points in Battles vs giving more material, am I wrong about this? Has anyone that is good with math looked at this?

I thank you in advance for your help.