My pump is more powerful than the overflow so I close the output ball valve on my pump until I get an even flow. Closing it a little bit at a time.
I have an evaporation rate of about a quart of water a day so when I look at my sump the next day it looks like the pump is pumping faster than the overflow provides(water level dropped). I add a quart and the water level is at the right height again in my sump and the tank.
So, Yes you have to do some fine tuning until you figure out your settings. Another thing that happens is when my filter starts to clog in my drip tray the water fills the drip tray and the level in my sump drops. So I loose about a quart and a half in the tray when its completely clogged and the water bypasses the drip tray. Filter change time and the level is fine again.
I have a 220G with a 25G sump. I'm running dual 1 1/2" overflows T ing to 2"....It pushes about 900GPH My pump will easily push 1600 Gallons at 5ft head so I have to cut it back a little.