The problem I do see is that the Ladder could be a bit steep when working on it taking into account of the width of the stair from wall to stair rail...
That is a good point - ladders at steep angles (or shallow for that matter) should be avoided, but is some cases there is little option. A bonus of
Tigger90's is that you could get a basic 3-way ladder closer to, and higher up, a facing stairwell wall, helping to gain access to those awkward points at the top centre of the side wall(s), if you don't have access to a longer ladder/boards.
(Not once have I ever had a 3-way ladder at a shallow angle, while standing sideways on the rungs, leaning backwards with a paint kettle in one hand and a paintbrush in the other, praying that my tonnage didn't buckle the ladder and cause a major catastrophe, just to save me the bother of setting up a more suitable means of access. Nope, No Siree, not me, never!!)