The real question here is what was meant by "increase GI". There is GI *quality*, which would be increased with the cache detail, etc., and would give you more *detail* in the GI, especially shadowed areas, and more accuracy. But then there is the "amount" of bounced light, e.g. brighten up the shadows, using either increase in Enviro Light strength, or Bounce to the Ounce (it is, of course, the corresponding setting to Occlusion Weight, allowing to individually tune the strength of shadowed areas and bounced light). Changing *both* at the same time, which is what you did, doesn't really make sense, though I understand why you did (after all "more GI" wasn't really clear to begin with). Just know that the GISD and Enviro Light settings are affecting *strength* of a GI component or effect, while the Prepass tab is controlling *quality* of the GI (i.e. detail and accuracy).
- Oshyan