Pompey
I may be wrong but I thought all 3 services now worked from the same allowance regulations (JSP700) and therefore regardless of whether you are on JPA or not everybody should be entitled to the same allowances and at the same rate. Sounds to me like you have a jobsworth admin person who is using the "you're not entitled" excuse rather than getting off their fat shiney ar5e and paying you correctly.
Personal opinion!
W