Raking light is the real specification
Hillside houses collect light from angles a flat lot never sees. Sun comes off the canyon, bounces off glass, and travels along a wall at a shallow angle for hours. That light finds drywall texture, taped seams, patched fastener heads, and the ridge where one roller pass met the next.
Two decisions control the outcome. Wall flatness comes first. A corridor wall and a west-facing great room plane call for different levels of skim and sand, and the sightline decides which. Sheen comes second. Higher sheen throws light down the plane and magnifies every deviation. Deep-matte and washable flat systems absorb it and hold the wall reading as one surface.
Our field team walks the room at the hour that punishes it most before specifying either one.