QuantumCabbage

Hey folks! I already tried posting on odforce yesterday but to no avail. I've got a question that, even after lengthy research still has me stumped. I've got a pyro fireball and a ground geometry that reflects the fireball. The simple question is: How do I set up the ground plane and its material so it reflects the fireball, including alpha, and just gives me a black alpha where there is nothing to reflect? I've tried to force it to phantom, that just makes it invisible, other, somewhat hacky workarounds like this one [forums.odforce.net] are rather old and in the SHOP context. Nothing I tried seems to work.

When I'm working in 3ds max and Vray, I use this technique all the time (vray object properties -> reflection/refraction matte), I just don't get how this can be this much of a faff in Houdini, so I'm probably missing something pretty obvious.

I'm grateful for any and all help, thanks in advance!