You need to remove divider 'D' because that will mean the water will be dropping on top of the return pump which will introduce bubbles into the pump. This will reduce pump efficiency.
Remove it all together as it serves no purpose at all. The water level will fine if 'D' is removed, as long as the overflow can outflow your pump(s) like a good sump arrangement should then it will be fine and the pump(s) will never run dry.
If you look at other sump designs they do not have a divider like your 'D'.