The water level in the tank will never change. It overflows, so it can't.
If your water level in the sump is that high, then you've a ticking time bomb waiting to go off, as if your power goes, you'll flood the sump all over your room!
The level in the sump should be just below, an inch or two below the baffle in the final section where your return pump is.
The chamber where your return pump is, should be THEE only chamber in the entire system whose water level changes. All other compartments permanently remain constant.
Take water from the sump until it's in the last chamber an inch or so below, and it'll all become clear how it works.