Running the same level in Marathon actually allows the player to squeeze a little bit further into that gap but it makes movement really glitchy so that's most likely down to a bug in Marathon. Also, fun little fact, the player sprite is actually larger than the collision shape.
I had some trouble attaching the gif to this post so I'll just link to the tweet. Sorry about that. https://twitter.com/johannesgunnar/status/1026081189403258885