First of all, fed funds rate is the rate banks borrow reserves' from each other. Interest rate on loans is the rate the bank charges to public for its loan. From one line of logic, we think of the rate bank charges to public should clearly be greater than the interest rate itself bear to borrow since banks are making a margin. And empirical data clearly support it.
However, another line of logic does not quite support it. We know the banks borrow reserve money in fed funds market, which is clearly better than the money it lends to the public in the following sense: one unit of fed funds can support 10 units of additional deposit if the reserve-deposit ratio is 10%. So the banks with this addtional 1 unit of reserve, can theoretically make 10 more units of loans and therefore creating 10 more units of deposit. So reserve is better money. Hence, theoreticaly, the fed funds rate should at leastbe higher than the rate banks make loans to the public, if not 10 folds.
My question being whether there is a logical fallacy in my understanding and if not, what kind of reality deviated it from theory.