From CA design perspective, it is making no sense to put a MC at a central office for a branch MA switch stacks. Typically a branch you may have 1 SPG & you better off MA/MC functionality within the same SPG.
If you have more than one SPG at your branch, then it is good idea to have a discrete controller at branch to do MC functionality (inter SPG roaming to be handled by MC). Instead, if you keep MC at central office these user roaming decision will be taking un-acceptable amount of time depend on the WAN link propagation delays.
Refer BRKCRS-2889-Converged Access System Architecture
Here are two snapshots from above presentation to explain this
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