When I used multiple keyboards...I preferred my most comfortable (best) keyboard, flat and at the best playing height. I also preferred to play left hand bass from the same keyboard in split mode...

If I added a keyboard for bass, it Sat on the left side just above the main board.

If I added another synth for color, it would sit above the main and bass keyboards, leaving space to change control on the main...I would tilt the color keyboard for visual and better playability..

I also kept my rack synth (midied) to the main and color keynboards, off to my right....mixer on top of the rack case..

I am so glad a single keyboard can do it all (G70)..😌