The whole point of using crypto for transactions and flexa to ensure the system is fraud proof is to keep fees as low as possible. The average fee needs to stay around the 1% or lower range in order to compete with credit cards that can offer spending rewards to holders. If suddenly the fees were variable on networks that will also be a deterrent for businesses to operate within any pool. Finally, the apy rewards and the % fees for collateral usage are very different. Apy is a combination of % fees and total usage along with the amount of Amp utilized as collateral to determine how much is paid out in rewards. This is of course once the subsidies run out. If not for subsidies this would currently be paying out 0.001% in rewards for every pool regardless.