It's not the placement so much as what direction the bug on the floor closest to the door is moving. I actually don't know which direction we want him moving, but one makes him easy to hit with a diagonal shot and the other doesn't.
You'd want him moving towards right, that way you can just fire diagonally and hit the critter. If he moves left, I think you're screwed for the spark... I say it's definitely a good idea to enter the save room just to assure you get the spark, you only need to take a few steps right inside the room and the spark is guaranteed.
EDIT:
Never mind. Guess what, Charge Beam has yet another use! What you wanna do, is charge your beam, and release the shot just before you pass the point where the angle of the slope changes (it's in the middle of those two purple pillars). That way the shot will hit the critter regardless of direction.
EDIT:
Never mind. Guess what, Charge Beam has yet another use! What you wanna do, is charge your beam, and release the shot just before you pass the point where the angle of the slope changes (it's in the middle of those two purple pillars). That way the shot will hit the critter regardless of direction.