If you want stationary light you need to set the light to be stationary mode.
In static mode, the ‘light’ is no longer there and the engine can only generalize 3 lighting directions that are always fixed in tangent space. So any lighting you have will be averaged into one of those 3 lobes so there simply isn’t much there for shading. The lighting at glancing angles suffers the worst because in effect the static lightmap pulls the light to always be a certain height above the polygon.