If Allowance for doubtful accounts increased why would allowance for doubtful accounts as a percentage of accounts receivable decrease as well?

If you started the period with 10,000 in A/R with a 1,000 allowance for bad debts (10%) and then determined that 5% was an adequate allowance but A/R at the end of the period was 50,000, you would still have to increase your allowance by 1,500 to a balance of 2,500.