The problem with the X factor is that it goes to everyone, including the fatty that has failed his fitness test and those rubber desk johnnies regardless of time in theatre.
It also goes to those who, purely because they're on the "wrong" unit or in the "wrong" job aren't "lucky" enough to be deployed. If you're going to make sure that everyone has the same opportunities to be deployed, you can justify what is effectively a drop in salary for those who stay at home. Much as l'd love the extra cash when I go on my second det this year in four weeks, I wouldn't want it to have come from the pay packet of someone else who was just as willing to go.
All I've left you with there is the option to recoup the money from those unable to deploy - hardly fair if it's a service injury, and impossible to get past discrimination laws anyway!
BCH