Please note that 100% of the BUSD that comes into the PSM from minting MOR stays in the contract waiting for MOR redemptions. No BUSD is used to buyback GRO. This alone further overcollateralizes MOR. This means that, for example, if 1,000 MOR is minted in a day, and then redeemed, the contract holds the 11 BUSD in spread fees for whenever another MOR holder wants to redeem for BUSD.