Is there any way to have multiple diffuse bounces (using the VEX gi light) in mantra without using PBR?

in the Irradiance section of the rendering parameter interface, there is this parameter: Max Gi Bounces (vm_gibounce)

What does this parameter control? (I didn't see it documented in the help)

I've tried but can't seem to get more than one diffuse bounce.

Thanks for any insight into this…