My brain tries to justify it in this way:
Your lightest spring is on your LR, therefore it would compress the most. The LR compressing lowers the LR ride height (relative to the the other corners compression). When you lower a corner height, you lessen its weight and transfer it to the other corners. Hence by moving weight from the LR, the cross weight goes down.
At least that is what my brain tells me. As I am relatively new, perhaps others with more experience could either support my theory or correct it.