Of the deposit account, they keep 10% in the vault/Fed, and loan out 90%. Of that 90%, they keep 10% in the vault (9%), and re-loan 90% of it (81%). Of that 81%, they keep 10% in the vault (8.1%) and re-loan 90% of it (72.9%). Sum the series, and the effect on the money supply from loans and the reserve requirement is to divide the vault cash by the reserve requirement to get the bank account totals.

Raise the requirement from 10% to 11% and the circulating money supply drops from 10 x vault cash to 9.1 x vault cash. Raise it again to 12% and that drops to 8.3 x vault cash. To keep things steady, you have to print extra money for the express purpose of putting it into reserves.

The de jure impact of the reserve requirement on the money supply isn't "not much"; it's actually huge. But that is only down to the point where it goes below the de facto requirement imposed by normal bank operations. You drop the requirement to 0%, and banks will still keep cash on hand to cover their own needs. It is certainly possible to raise it all the way to 100% (or even higher, by requiring that banks freeze some of their own cash when accepting a deposit). But that would have to be done very slowly and cautiously.