If you believe that going to an airport, checking in and travelling as a pax for a 2 hour sector should not count in the slightest as FDP, then you also believe that I can be called in by my company, shoved in the back (as a regular pax) for a sector, and then have my FDP start down route.
With all respect, let's turn your argument around. Sitting on a couch at home watching tv or surfing the net does not generally have an effect on FDP. You could do that all day long and then report for duty operate a Sharm. So, using your above argument against commuting, time spent for example on
airport standby should not count towards FDP. Some even manage to sleep on that couch, or sip Coffee in Costa for hours.
See the flaw in your logic?
Wether or not something counts towards FDP has more to do with the question who is in charge of that time than what is actually being done. As a commuter it is my decision to commute and I commute in my own spare time in a way I find suitable. Positioning however, like airport standby, is done on behest of the company, they tell you what to do and how to do it, wether you want it or not, wether you are tired or not. Hence the FDP clock starts ticking and rightly so.
So I don't see any reason why commuting has any influence in FDP claims towards positioning. To me that's seems a bit far fetched.