According to Mishnah Berurah (OC 131:13, and quoted in this answer), if one is outside the shul, but the door to the shul is open, and from his location he can see the place of the Aron, he should do nefilat apayim.
What if only one of these criteria are met? For example, the shul is L-shaped, and he's in the corner of the L where the Aron isn't visible to him, or he's in the courtyard of the shul and the door to the shul is closed, but the door is made of a glass pane through which one can see the Aron (or if he can see it through a window which is closed with a glass pane). Would the fact that he's still in the same room, or that he can still see it (albeit through glass) be sufficient to require him to do nefilat apayim?