This still sounds to me like you are charging her an extra day for each day she wants to switch.
If she can't take the boys and so you do, then she should have a day in the bank to use at a later time, not you.
I've never heard of divorced parents handling custody in this manner. If I were her, it would seem to me like you were punishing me and also trying to erode my relationship with the boys.
Me: 44 H: 44 Kids: 20, 16, 16, and 10 Together/Married: 22 years H announced he was emotionally detached and considering D: 4/4/16 H announced he is going to try to stay and reconnect: 5/1/16