TBW
I think, with my experience and the benefit of hindsight, that retention is far more complicated than just a fun/pay balance for most. Prospects for continued engagement into full career and/or promotion were always important, coupled with options for a civvi change-over if you needed to. Whatever, the plan now seems to be: get them in for as short-as-poss to avoid paying much or building a pension and, it'll be fine, Honest!
OAP