I think this has to due with your cell size. Your walls/blocks are multiples of 44(ish) but your pathfinding cells are 30+6, so 40. I would suggest sizing everything appropriately, turning on the grid, aligning with the grid, so that everything is lined up with the grid. Reread the documentation on the cell mechanism. I did a quick experiment and it did seem to improve (I did see the overlaps you were seeing prior to these changes.)