You have to remember this setup is tiny, this is a freshwater system that needs a very minimal flow not to disturb my fish. I understand everything on the overflow/emergency side all needs or should be of same diameter, but the return:export system ratio is what I am asking about. Dual 3/4" return jets are massive for these tanks, they are basically 10 gallon tanks. I would think I can have a smaller return pipe then exit, I planned to have nothing larger than dual 1/2" return nozzles on each tank. Having two on each tank brings the flow rate down on each to spread out the disturbance and provide redundancy. I barely need the water to exchange between the two tanks for stability, I run my systems borderline walstad but I have the principal down and my tanks are very clean.
I will look into the principals of the bean again this evening. The system I had in mind used two 3/4" lines, one main gated down and the other was placed higher fully open for emergency only.