Firstly, I assume you want Pilot, yes?
Having been on a UAS for 2 years and been for selection last year I can say that filter interview for attending OASC is pretty similar to that for UAS selection. It does, however, get much more competitive at OASC.
Regarding aptitudes, with the extremely fierce competition (to quote OASC) for aircrew slots, this means that a 'pass' is no longer sufficient. It has been sugested that a realistic figure to be competitive is something circa 150-160. However, there are many other factors.
I would suggest that you look at why you were unsuccessful at getting a UAS slot since as I stated eralier, UAS selection is a mini version of the full OASC procedure.