Cooler float valves use a paddle arm that screws to the float valve and adjusts at the pivot point with a screw.
The problem is if the float valve is mounted high above the level of the water, such as on these larger commercial coolers, the float paddle is not resting on the water line properly when you simply angle the arm down for adjustment.
You MUST bend the arm to correct the angle of the float paddle where it contacts the water. This gives the most leverage and force against the float valve (which has water pressure trying to push it open) and will allow the float valve to open more and close more while requiring less water rise.

If the paddle is just bent down into the water, the arm can be adjusted to get the float valve to close (although piss poor) however the progression of the leverage against the valve is increased and there will be less float arm travel as the water drops when the pump starts. When improperly adjusted the arm drops the valve will not open as far and there will be a limited gpm water flow. The cooler may even evaporate so much water that the gpm of flow is not enough and the arm has to drop even more.
And this may even cause the water level to reach the lower section of the pump and cause starvation until the water level rises and the pump can prime.

The level is much better controlled with the paddle flat on the water line.
Only about 1/2" of water drop will be required to get that float valve to open at a higher GPM rate and in reverse only a 1/2" rise will be required to again close the valve completely.