[kach22i]

I believe the prevailing wisdom on blocks (grilles and open fog-light opening etc..) is that you can do them at front/top surface or behind the opening.

Reason for this is that a pocket of pressurized air forms at such recesses and air flow goes around such pockets of air, similar to a half covered pickup truck bed.

Just say'n if you want to be stealthy with your work and can do it behind it's an option.

I think the reason you see blocks from the street-side is easy to see what you are doing, and zip tie to what's behind it is cosmetically simple.