Great thank you!
I wasn’t aware that the component was treating brep and mesh input differently!
I also found that now (maybe it can help other people):
“When you connect up breps, the component uses the _gridSize input to mesh the geometry based on that grid size but, if you input a mesh, the component will use the existing faces of that mesh and perform radiation analysis on each one of those faces.” (https://www.grasshopper3d.com/group/ladybug/forum/topics/radiation-analyses-grid)