Are they basing these "fare differences on what you actually pay or on a published fare? For example does a forced downgrade on an AONEx on a confirmed booking in A get the same compensation?

Personally for me the downgrade from long-haul J to regional J is at least as bad (on a lkong haul flight such as SYD) as an F to J downgrade (you lose a flat-ish bed, and the AVOD), but just a few AsiaMiles for that, and only if you moan.