Where do market premiums for scarce skills sit in your adjusted gap model?

Semiconductor equipment company, about 2,000 employees in the Netherlands and Germany. We pay a market supplement of between 8% and 20% on roughly 260 roles, mainly process engineering and embedded software. Those roles are 84% male.

If I include a flag for supplement-eligible role, the adjusted gap is 1.6%. Without it, 4.9%. The supplements were set from survey data and I can evidence them, but the list of eligible roles has grown by negotiation over five years and I doubt every entry would stand up.

How do others treat premiums: as a legitimate control, as part of pay to be explained, or something in between?