Hm, [@Oak7ree], you have a point.  And I"m not having another idea come to mind.  *grumbles*

Right, so how about this: during whichever mission ended up being their last, Bel and Izkry split off because sniper and not the best at meshing with the team.  Bel makes them uncomfortable.  Sparks is her spotter.  Anyhow, when the muck hits the fan, they're not with the rest.  They do what they can to help, but...something something, maybe an explosion that takes everyone in a certain radius?  *shrugs*

With their team eliminated and no good way to proceed, the pair are called back to base, but it's not easy to replace stuff like that on short notice, and they're left at loose ends.  They were already permitted to leave Switzerland to join the British venture, so perhaps they are either requested or it is suggested that they go help with the American one.