Light leaking on baked lighting

I am setting up walls to be used with substance designer materials. I want different materials on different parts of the walls.

When I bake the scene, I get shadows and light leaking through the different wall segments, you can see in the image how the different segments are broken up by hard light changes. Why is this happening?

I have tried doing this with both planes and cubes. Cubes yield better results but I still get hard light change at the seems. I have also tried overlapping them a bit, but that has other issues such as textures blinking when overlapping.

I know one option is to create the full wall in Maya and dedicate different material slots to each section of the plane. I could do that, but I am trying to find all the ways I can make this work.

Am I going about this very wrong, or is there some way to fix this?

Setting Baked Resolution in the lighting window to 4 seemed to help a lot! I had it set to 1 for speed… serves me right!