Ref item 2, this only applies if the normal journey time from the accommodation to the airport is less than 15 minutes. How many people actually live within 15 mins of the reporting point at base, especially at LGW / LHR / MAN. Travel from car park to reporting point exceeds 15 mins most days.
Item 3 will work both ways. If you check in overseas at 0630 local then yr FDP wil lbe based on 0530 local, i.e. 2 hours less. However, if you check in overseas at 2230 local then yr FDP will be based on 2130 local, i.e. 1 hour more.
Duty and day off totals on a rolling period basis is fair enough. The roster week dates from the days when flying was done Mon-Fri with weekends off. It is going to make an impact on some of the charter cariers though