dusk2dawn, postflight allowance is not much connected to the completed FDP, it rather used to make your "off-duty" timing realistic which is in turn affects the start of your next FDP (min required rest). I would say most EU operators FDP I've seen call for 30 min post-flight to be accounted into FDP, thus max allowed FDP is always 1.5 hrs more than actual production.
In my company (we use EU-Ops) Flight Duty Period ends at block-on, the next 30 minutes counts as Duty Time.
