/ic/ - Artwork/Critique

Perspective question here. Just analysing this painting while going through the Olson course. The box being leaned on (with the question mark) is not in the correct perspective technically right? I'm under the impression it should line up with the dark purple lines I made over it, but it doesn't- have I missed something here? I assume if it is wrong it was just done this way because it looks better like this (which it does). I'm still early in the course so I could be missing a big thing here, please let me know.