In the RRG:

"When attacking a door, using an ability that affects a door, or counting spaces to a door, the door is considered to be occupying each empty space with which it shares an edge."

So (using FizzGrid ^TM ), can the Stormtrooper target the door ( | ) from here? B is blocking terrain, or figures, or something you can't draw LOS through.

[_][_][_][_][_]
[_][a | [c][_][_]
[_] [a | [c] [_] [_]
[_][_] [_]
[_][_][_]

Does he need to draw LOS to the corners of the "a" spaces, or the "c" spaces? And what if units are in the "c" spaces? Can he still attack the door then?

Is the door between the a and c spaces? If so, S can draw line of sight to the top c space (both right-side corners), provided c is empty. (And even to top c's top corners). The required accuracy is 3.

If the top c is not empty, S cannot target the door from this position.

Okay, so you can still block a door by standing in the spaces next to it, because the they aren't "empty spaces," as the rule says.

Thanks!