Two, there is no magic number for a deposit insurance fund. The test of an insurance fund is not how it does in good times, but how it does in bad times. Today, the Bank Insurance Fund has a reserve ratio of 1.38 percent. Since 1991, the reserve ratio has varied 174 basis points. Big enough to do the job.
History offers a cautionary tale in that regard.
As we learned in the late 80's, the deposit insurance funds stand between bank failures and the American taxpayer. The Bank Insurance Fund reserve ratio has not grown in the last three years. While the amount of money in the funds has grown, the amount of deposits the insurance fund must cover has grown also. Deposit growth can affect the strength of the deposit insurance funds significantly. Deposits fluctuate - sometimes greatly.