It is sandwiched top and bottom; capping off zone A, and riding the niche around the outside of zone C. If it helps, consider two horizontal plates, one with a hole it.
Hmmm... Let me ask this way: what is the biggest player when it comes to orienting and locating this part in assembly? Two plates and the hole OR the plate with the hole only OR the piston OR the cover plate at the bottom?
The part would pilot on a large diameter concentric to the bore that the piston is in, sliding the zone c end into a hole until it rests on the mating side of the coverplate covering zone a.
The bigger issue is in the portion isolated and presented so far. It deals with the amount of rotation the piston can encounter. If you study the extended context, detail c[5], the piston has been rotated ccw. The challenge is keeping the smaller slip fit diameter concentric to the larger one.
So why did not you consider controlling position of the bore in zone C relative to the bore axis in zone A from the very beginning?
If centering is your main concern, what is the reason behind applying position tolerance at MMC/MMB rather than at RFS/RMB?
