OTOH, sitting even further back, with service personnel earning far more than their CS boss one could challenge pay rates on employmeny law basis.
I believe this has happened successfully where a female supervisor was being paid less than her male subordinates.
In the military case it would be necessary, in UK, to separate out the X-factor, the 7/24 hr commitment etc, to prove that the serviceman was, pro rata, on a lower pay rate albeit had significantly higher pre-tax, take-home pay.
Overseas the distinction, say inside the safehaven, would be finely balanced and the C2 CS should, everything being equal, be paid at the same rate as his military equivalent and so on down the line.
Could be interesting if the unions decided to take that one up.
Now where's my flak jacket, oh !!!!!, I handed it in.