There is almost never a banded tournament without some rebouncing high-ranked player participating. We all know that he'll most likely win, because ones chess skills don't disappear overnight, little less over 30 days. However there is also the aspect of winning streaks to take into account especially for players ranked in the area that the banded tounaments cover.
My proposal is this:
Remove the time-limit regarding highest rating used to determine eligibility for rating controlled tournaments. But ad a time-limited buffer-zone on a specific number of points, which I would set to 150 points. This way you would still be able to participate in a 1200-1299 banded tournament even though you reached 1370 in rating two months earlier.
But it would prevent 2000+ players entering banded tournaments after a four (or whatever time-period) months break, because the buffer-zone only allowed them acces to banded tournaments 150 point below their previous rating level.