With reference to the answer given to Appendix 4 Research Questions, Q10:

Answer (b) "Any positioning flight, before or after a FDP, must be considered to be part of the FDP and the normal FDP limit that applies must be reduced by the duration of the positioning flight." (Appendix 4, para 7)
and,
Bob Tait Appendix 4 Summary,
5. Positioning - If a pilot is required to undertake a positioning flight (that is as a passenger, not a FCM), the duration of the positioning flight is to be included in the FDP before or after the positioning flight.

However, para 7 only states that "On completion of assigned flight duties in an FDP (the relevant FDP), a FCM may position to a suitable location as required by the AOC holder", and

6.3(d) in the Definitions of CAO 48.1 says that,
"Positioning, if undertaken immediately after the person's flying duty and no other flying duty is to be conducted in the duty period - is not part of his or her FDP"

Q:Does positioning after flying duty count as part of the FDP?

I think the wording in the Bob Tait Appendix 4 Summary is not completely accurate.

The definition of FDP in CAO 48.1 states that the FDP:
"(b) ends at the later of:
(i) the person’s completion of all duties associated with the flight, or the last
of the flights; or
(ii) 15 minutes after the end of the person’s flight, or the last of the flights. "

As you identified, positioning before the FDP is considered part of the FDP (and the reporting time for the FDP includes this). Positioning after the FDP "is not
part of the FDP or off-duty period. However, it is added to the FDP for calculating off-duty period
requirements.".

It is also "is duty and part of the duty period.". (CAO 48.1 Para 6.3)

So positioning after a FDP is considered part of the duty period, but not part of the flight duty period.