I think that a CO BF/ AF J combo will be 100k. AF J is 50k/per on a standard reward.

As for "backtracking on a reward ticket," it is totally permissible. The OP agents totally understand maximizing the FC/BF experience! ^ I flew CO/AF from IAH-LAX-CDG on a reward once (in Y, I don't know why....I was much younger and "hey man, I'm on a plane!! YEE-HA!)

I did IAH-PHX-EWR-SXM last year with the IAH-PHX-EWR as a redeye to save $ on a hotel in EWR (due to the early departure of the EWR-SXM segment). No problemo!