...Wow, Guess you're right, It works ok even when you assume it's square. What happens if you drag the green ones to something we know 100% is gonna be square? (i.e the vertical-y part of the bridge)
The scene is actually square as seen by my pictures above. You just have to get the perspective right.
While possibly the most embarrassing way I've ever turned out
sort of correct, I noticed the walls still don't line up perfectly like that (you can see a bit of the reactor's face painted onto the wall, as well as a sliver of distant ground). I guess that's getting a bit further from my assertion that it's "illogical", although still a bit quirky if someone wants to go for total accuracy. I made it way harder than it had to be by not having the the base and top edge of either wall parallel to each other though.
