Well, the lack of clarity lies in the definition of flight duty time at least in the german version of the EU-OPS (which is applicable for me). The definition 1.5 in OPS 1.1095 says that the flight duty time ends with the end of the last flight of a duty period on which the crew member is on duty. However when the flight ends was a point of debate. The local CAA now clarified it and said the flight ends with on chocks. Everything you do after on chocks is not flight duty time anymore (except if your personal or union contract says anything different), but until all work pertaining the flight has finished it is still duty time which in turn is relevant for rest time calculation.
CAP 371 of course is only applicable to UK carriers and quite uninteresting for the rest of europe.
And i do disagree with your view of 1.12 as it says that positioning is the time spend during a transport from one point to another, however the time spend travelling between your place of residence and your reporting point (usually the crew room) and the local transport between airport and hotel is not positioning time but "travelling time". Travelling time however is part of your rest time and accounts for the 2 hour higher minimum rest time at your home base vs. on the road (2 hours travelling time, one hour after and one before duty). Travelling time is accounted for in OPS 1.1110 1.2 which says that you have to have a possibility of at least 8 hours uninterrupted sleep time plus time for physiological needs and travelling time. Physiological needs is often defined as one hour before and one hour after your sleep time period. However physiological needs is another one of those gray areas as there is no definition in the EU-OPS.
As someone who works actively in the union on matters like that is often quite distressing how many gray areas are there, especially when you count in the differing views of your employer, the local CAA, the ministry and of course your union. It is not an easy field by far and quite often we wish we had CAP 371 which seems in many cases quite a bit clearer than our local regulations.