OK.
I'd take the open window in the cubby hole any day of the week, like they did on the fifth floor.

BRW said that he was expecting the others to come back up to the sixth floor to watch the motorcade. And when they didn't come back up there he decided to go elsewhere to see if he could find them. Also, the sniper's nest was a pretty tight squeeze even for just one person. I cannot imagine three of them trying to get in there between the windows and boxes. And, apparently, they could open windows as needed, the windows were open on the west side (where they had been working).