Kiltie,
Took up your first point with a NATS manager, who assured me that the MATS Pt 1 takes precedence over the CAP413.
Another aspect which may confuse the issue is NATS annoying habit of introducing extra bits and pieces of verbiage as company 'best practice'. Can't be arsed myself to look up to see what they say about pressure settings. Any other NATSI's know if the Reichstag has anything to say about passing QNH?