20H gallon as a sump for 92 corner tank?

[CaptNemo]

Hello all,
I am helping to set up my brother tank, it is a 92 corner oceanic tank. I wanted to get a 29 gallons as a sump but it doens't fit under the stand. The only thing that it would fit is a 20H gallon. Do you think this is enough? I just need the sump for the skimmer and the return pump, not going to use any part of it as a refugium at all.

I am afraid that since the sump is so small, the force of the water of the drain will interfere with the skimmer. When I used the Coral SS 220 on my old tank, if the water level of the tank go up and down, the skimmer will stop working and overflow.

What kind of sump to you guys use for your 92 corner tank?

I plan on partition the 20H tank into two part:
the first part will have the length of 18", this will be for the drain water and the skimmer.
The second part will have the length of 6 inches, this will be for the Eheim pump.

The partition will be of three pieces of glass, over, under, over.

Do you see any problem with the way I plan on partition my sump?

Thanks alot.