The Processing Fees that donors can cover reflect the actual processing fees paid by the non profit. This would adapt based on the payment choice they make - whether credit card or ACH. This would be calculated and displayed on the checkout experience for the donor.
I was about to submit a similar request. Right now it looks like the "cover the fee" checkbox defaults to 3.2%, but it should be 1.8% for ACH. I think part of this is because the "amount" page precedes to "payment method" page. If it were all one page, the fee could be dynamic based on amount AND method. It also should be noted that the 3.2% does not account for the extra $0.30 fee.