The problem is primarily that the light source is a point light centered on the empty block space adjacent to the light block, so it's easy to just remove the point light when the adjacent block space is filled with something. Therefore, modified light sources would need to be introduced to fill in the gaps. Here are some recommendations on how they could introduce that new lighting.
1. Wedges, corners, and tetras: point light at approximately 1/3 intensity (~85/255) at the "centroid" point between the three "exposed" points of the block. At this scale, the centroid could probably be approximated as 1/4 of the distance from either open side.
2. 1/4 slab: 1/2 intensity point light 3/8 from the open edge of the space, which is half-way along the 3/4 space that is -not- taken up by the slab.
3. 1/2 slab: 1/3 intensity point light 1/4 from the open edge of the space.
4. 3/4 slab: 1/5 intensity point light 1/8 from the open edge of the space.