Sagging cover

Not quite as much as yours, but my banjo tight when dry cover did a similar amount of sagging last week. That storm was wet snow and ice. Very heavy stuff eventho it was only a few inches. The cover itself stretches some once wet/saturated and then the weight of the snow pulls on the springs. Some years a similar storm will pull the cover down to the water level like yours and freeze it there for a month. It can handle it fine.

If we get a warm spell and everything melts you can double check that the springs are about half compressed when the cover is bone dry. You are ok either way, but some extra piece of mind never hurts.