I think a sarcasm gone unnoticed is the writer's shortcoming not the reader's.

Adding a horizontal reflecting shelf the length of the hallway is far less likely than lining up reflections. It doesn't even make sense.

If you start with the hallway floor and then mark out the same distance as a reflection it all matches up.

Yeah I saw it as much wider at first too, with those doors to the left sort of floating in apart from a wall.

Thanks for the looking tips