It might be just around the corner from the ship (ironically) but not from the room they have just snuck into.

Remember we are talking in three dimensions here.

Ben doesn't know that until they get into that room and if he did and he just nipped out, dodged all the guards on the way in, switched off the beam and sneaked back, Leia would have ended up as pink glitter when the Rebel strike force finally managed to catch up with the station after searching around the cosmos for signs of obliterated worlds (assuming Vader didn't put the homing beacon on the ship the moment it landed).

If the fight was edited that way there could have been a lot of space covered that we wouldn't see between each location so it needn't be right on top of the hanger.

One presumes it's pretty close as we don't see Ben catch a train or take much in the way of elevators and he is a bit conspicuous (sure he could cloud the minds of many people who might notice an old guy in Jedi robes walking around but someone would notice him eventually if he has to travel a great distance).