We houseruled the non-diagonal movement and opening of the doors. It just got out of hand in our games. Not only that some scenarios only require one vanguard to reach a certain square, the cheesy tactic to put minis behind doors and have another one open it from the side so they could fire with focus without triggering a reflex from the opponent felt wrong.
I have yet to play the game, but what you describe sounds incredibly thematic. I imagine a "Rainbow Six" team stacking up on a door and one person opening it and the team achieving the element of surprise.
Also, I thought reflex triggers happened when a model took an action in another model's vector? Is it only a move action that triggers reflex?