"Rays" are only going to show up when there is a medium to show the difference between light and dark; they are, quite literally, *shadows* being cast into atmosphere. So they depend on atmosphere and/or cloud and while normal rays from a cloud can work without Receive Shadows enabled, from an *object* you would need Receive Shadows in either the atmosphere, and/or a cloud layer if you were using that to easily increase local haze density. Keep in mind that both options will significantly increase render time.
Bottom line: I'm highly dubious about trying to use bounce setups and other traditional lighting approaches that are focused on small scales within a TG environment at large scales. While it may be possible to get the effects you want, you're going to need very high GI, and possibly other options enabled like Receive Shadows (for your rays, at least), which will mean very high render times. There are tools like Enviro Light Strength on Surfaces and Luminosity that are designed to address subtle lighting issues like this.
- Oshyan