If you mint more RAI than the amount of RAI you provide as liquidity, you only accrue rewards on the amount you minted & LPed. Likewise, if you add more RAI as liquidity than you mint, you accrue rewards only on the RAI amount that you both minted and LPed.
In short, you can think of mint + LP as a formula:
RAI Eligible for Rewards = min(RAI from LP token balance of an address,
Total RAI debt from Safes owned by the address).