Effect of higher wound screw vs slug coil in offset humbucker?

[Stratz]

I'd bet that the overall permeability of the slugs is higher than the screws. The portion of the screw that sticks out of the top and bottom contribute slightly less to the inductance than the permeable material immediately inside the code, and the screws put more "air" between the metal and the windings than the slugs do.

Ive found that the inductance is extremely close with both screw and slug coils wound to the same number of turns and loaded with the screws, keeper bar and slugs.
From my experience the difference between the two is negligible.