A step in the right direction. Perhaps the same logic could apply to the amount asked for, where the fee is a % of the total amount requested?
If the added fee is flat for any daily amount, it will affect a modest proposal for ~15-50HBD and encourage asking for higher pay in shorter time. Imo, I quite like the idea of having multiple proposals for community work that ask for modest sums as a way to replace the need to use upvotes to fund activities. For them, needing to re-do a proposal all the time would be an unecessary cost.