I would say 'it all depends'. So you are medically downgraded but you don't lose out on your pay? Try telling that to aircrew.
No it depends on how you are paid. If X-factor was separated out from pay then it could be paid seperately. Someone fully fit, or fit enough, for all the SH1T jobs gets the full wack. Someone with the 'no deployments' chit has their case evaluated.
Tescos was looking to penalise sickies, why not the armed forces?