Lightmass Inconsistency Among Bordering Static Meshes

In my scene, I have 3 adjacent static meshes designed to be two walls and a floor. The static meshes are one sided and intersect at the corners of each room with no overlap:

As is displayed in this picture, the seam between the forward wall and the floor is smooth and expected (with the only darkness due to AO). However, on both of the side walls, the baked lightmaps seem to be strangely dark and result in inconsistency when a mostly uniform material is applied:

How can I make the lighting appear more uniform and what is the cause for this?

This looks like it might be a lightmap UV issue. Have you made sure the UV islands not too close together, and are at a good resolution?