Two simple tools to use for use in debugging.
Remember these will impact performance if used on large grids as they draw text in the scene view.
Draw Cell Positions
Checking this will enable you to view the centre position of each cell, and ultimately the position that is being checked to see if the cell is empty or not.
Draw Grid Positions
Checking this will enable you to view each point created on the grid.
This will only draw the boundary lines for the grid instead of every row and column.
When working with extreme size grids this can be useful for keeping track of the object while still keeping a decent frame rate to work with.