I need help with the Impromptu Fire Propagation blueprint

How do I apply damage to the grids by projectile so A-The fire stops Spreading
B- The scorch decals remain

I’ve been messing around with settings for the past few hours, and haven’t been able to successfully do so.

I can easily apply damage to other objects but not the grids, if possible I would like to apply damage to each grid individually

Thanks in Advance