Sounds like your overflow or bulkhead (whichever method you're using) is perhpas too small. As you know, its function is to 'put back' whatever water is pumped up from the sump. As long as the overflow/bulkhead is rated slightly higher (higher being better) than the pump's rating, you should never have to fiddle around with ball valves(?) to control your pump. (not too healthy for the pump either)
Even if you get lucky and level it out for the time being, murphy's law will provide you with a change in variables (a stupid snail clog!) when you're at work and you might come home to a wet floor!
As long as your overflow/bulkhead is bigger than your pump's ability, you'll never run into any balancing headaches like this. You would just run your pump at full throttle and that's it. The drain will 'take' whatever your pump dishes out.
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George
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