ok.
My answer is:
Case 1
c. Wake Turb 'volume' is theoreticallyonly behind the aircraft generating the wake to a width of 1nm (therefore 0.5 nm either side of track). As long as an aircraft separation standard is kept, in this case 3nm, the wake turb 'volume' only descends with the aircraft as it desends.
Climbing up through through the wake trail is of course a different matter, and the appropriate wake turb standard then needs to be applied unless you wait until once again 0.5nm clear on the other side.
Case 2
a.
and
c. for the same reasons.
The reason I pose the question is I am amazed by the number of people (controllers as well as pilots) who insist the standard (theoretical, not practical) requires 6 miles before descending the heavy. This suggest that somehow the whole volume of wake 6 miles behind descends in unison with the aircraft ahead, instead of on a sloping trajectory.