Submersible pump dongle?

Born Yesterday's suggestion will result in the pump coming on in shallower water (probably good) and with adjustment (perhaps tedious) result in water level dropping into bowl, but not draining it, since the float merely holds a tilt switch.

To actually get the result you describe (many inches of water down to zero or nearly so) requires a different kind of switch where a float slides on a rod an turns on the pump switch at the top and then floats back down on the lowering water level until it hits another stop that finally turns off the switch. So it runs through the time to drain several inches.

Some refill valves on toilets (non-electrical) work like this.

TRY THESE.....

[1]CLEAR AWAY ANY GARBAGE OR DIRT THAT BLOCKING THE FLOATER .

[2] ADJUST THE FLOATER LEVEL SO THAT IT CAN ACTIVATE AT LOWER WATER LEVEL.

[3] CHANGE THE WHOLE PUMP.