Brassia & lava rock

[KarlBrown74]

Hello, new to the forums.

I recently acquired a pair of Brassia.
I repotted one in a name brand orchid mix, and I'm really not happy with how wet the mix is staying.

I keep my phal's in a mix of 75% 1/2 inch red lava rock, 25% coarse fir bark.

My question is-
Is lava rock (fine 1/4 inch) good with Brassia?
Would fine river rock be a better alternative?
I'm concerned about the coarse nature of lava rock damaging the fine roots of the brassia.

Note:
When not on display, I keep my orchids on humidity trays under grow lights.