Tiny Gaps in My Shadows

I'm trying to import DexSoft's Castle model into Unity. However, I'm noticing that all shadows have gaps where light bleeds through:


I'm not sure what I can do to avoid this. The model is airtight (no gaps, T-vertices, disconnected quads), though I'm not quite happy with the polygon topology:



Is there anything I can do or tweak to make these gaps disappear?

 

It's the normal bias on the light, turn it down to zero. Alternatively try setting the mesh as a two sided shadow caster.