Try fewer trays. One for developer, one with a water rinse/stop. Drain the rinse tray and add the fix. The drain that for a second fix, or reset to water for the next print. Fixed prints go to the washer or a holding bucket. That's the extreme end, but up to 11x14 prints it is easy enough to drain and refill trays. It gets harder with larger sizes.
I have a three level stacker that will hold 20x16 trays, but to be honest it spends most of it's life under the wet bench as shelves to hold the trays. I can just about squeeze four 20x16 trays on the bench if I move the Jobo. The big problem with the stacker is how much (or how little) of the lower trays are exposed. Big prints are not easy to slide in without creasing if the exposed portion of the tray is too small. It can be done, though.
My ideal small space stacker that I was planning before I managed my current darkroom, would have two trays below, one tray above. The upper tray would slide left to right so it could be positioned above either of the other trays. The top tray gets developer, the lower two stop and fix. The upper tray is moved to allow access to whichever lower tray is needed, so the overall width is around 2.5 tray widths.