Boundary zone can't be combined as such - the oyster or contactless card (the card you use for the section of travel not covered by the freedom pass) needs both a "beep in" and "beep out" to charge the right fare. If you beep in with the freedom pass and beep out with the other card you'll pick up a penalty fare.
If you get out at E Croydon and beep in there, you'll pay £5.20 peak or £3 off peak - that off peak fare is lower than anything currently available.