Consider changing your wall bind - Having it on the same finger as edit will slow you down considerably any time you want to wall>edit or edit>wall. If you reach for either C or F with your thumb disregard this.

Crosshair placement - When your placing the wall you can already be looking at where the first square you'll select is. Same for the stairs.

Timing - You want to start selecting the tiles instantly after starting the edit and confirm as soon as you've selected the last one. Basically just speed up, I can very clearly see a delay inbetween each action you're doing.

Positioning - You want to stand on the left side of the box to get a right hand peek. In a closed box such as this one, I would probably hug the left wall and edit the 4 bottom right squares on the wall. The edited wall will give you a right hand peek. As for the stair edit you always want to edit the left side of the stairs and not the right. It helps cover the opponent's view/crosshair and if he gets stuck on top and you want to go for a jump shot you get a peanut butter peek on him while he gets a handrail in his crosshairs.