Have you read Rick's core torque thread? http://www.discussfastpitch.com/softball-pitching/16719-creating-correct-core-torque.html
From what I recall BM has advocated the foot landing at 45. And a 45 degree hip angle at release. I don't remember anything about landing with the hips at 45. I think the foot angle is directly related to having it in a position where the hip is free to rotate a little into release. When it is at 90 the foot will lock the leg and prevent any hip rotation or at least restrict it.
As for slamming the door, that is just a misguided cue aimed at getting core torque. It is misguided because if the hips do indeed slam shut then the arm is in a bowling position at release.
To sum it up I would say you want to get open so you have enough room to torque the core for power while still allowing g the arm to be in a position to effectively internally rotate and the body to effectively adduct into release. Close too much and you kill addiction and I/R. Close too little and you leave core power untapped.