You also have to consider the more water you put on the rocks, the rocks start cooling down so you just won't get that steady state of steam.

I've actually contemplated putting a small pot of water on top of the stove in lieu of the rock basket. I'm curious if I get that boiling if that will give me a steady stream of steam.

@freerangepapa Any advice?

Are you letting the rocks get hot enough? After a few minutes I usually start putting water on and it gets pretty steamy!