Hi Wrinkles ,
except for the stand you’re using, the idea seems to work, both keyboards are probably as close as you can get to each other.

If I didn’t already have a stand for my p121 piano, some sort of a table for the bottom keyboard then a platform for the second, similar to what is in your photo of your first setup, would be something I’d try and do.

I used to use 2 keyboard stands at different heights ,and it sort of worked, but with the piano stand and trying to put a keyboard stand behind it, just didn’t work.