This is probably old, and probably also impractical, but it seems like a good, arrogant way to land an Astral Heat:
6A (jump cancel), jC, jD, jC, j214C, 2141236C
Damage: 2069, 17070 after Astral
Obviously, it requires Astral Heat conditions before you hit the 6A. I kinda suck at Ragna, so you could probably get j214C to hit a few more times by getting higher in the air. I only ever get like 6 hits off of it. =/