I find that when seating in 1k, the light from the first window in 2k will slip through the gap between the side-wall of the plane and the divider and it is really contrasting when all the blinder in 1k is shut.
If there is no one in 2k i will shut it as well (to give an idea of how close it is to the 1k seat - i can reach and shut it from my seat through the gap). But if someone is in 2k i will just put the cushion to block the gap.
I have never sit in 1A of 773ER but i suppose it will be the same as well.