You can change the bounce intensity by increasing the indirect lighting intensity on your directional light.
I haven’t been able to get heightfield GI working on 4.12 or 4.11 for some reason; I configured everything and see it taking performance in the profiler, but was seeing no visual difference, even in the visualize GI view. On 4.8 I am able to get it working and see it within visualize GI and within the game.