My enclosure is actually open at the back. It fits in, but just barely. Look at the 220v power cable. I wouldn’t bend it any more. And the heating bed cable would be compressed even more if there was another plate at the back. Due to the current problems with the heating bed cable, I would advise against using a plate at the back. You can’t push it further forward because otherwise the print bed will push open the front window.
The last photo is with heatbed full extended
Your see there is not much room