Make doorways remain open until shut. This makes it significantly less complex to perform basic CQC, since entering rooms in stacks and having the doorway shut on 3 out of your 6 operatives/partners in crime is an extremely easy way to mess up coordination, expose entering fighters to increased risk due to the lack of ability for anyone on the outside of the room to cover them, and scanning rooms before entering becomes basically impossible.

TL;DR Make doorways remain open until shut.