I think that would only be correct if the load on the circuit was
balenced e.g. at the mid point of the ring. If you put the 32A load
within a few mm of one MCB I don't think you could draw much above
32A (at least not for long) before the 32A MCB trips but this is
still above what the cables rated at since most of the current would
be travelling down the shorter (lower resistance) leg. In summary
your protecting the cable at 32A but the circuit between 32&64 A
depending on where the load is.

The overload tripping current will be very close to 64 amps (probably over),
the impedance for an overload current will have negligable difference
anywhere on the ring main cabling - (Kirchov's current law if you want to
look it up and work it out exactly)
If it was a short circuit current then then the difference in the impedance
would have a measurable effect but then the short circuit current would be
only for a very short period of time and into the thousands of amps range.
It is a very serious fire hazard in an overload situation as this could be
applied for a long perion melting the cable. It is also a bad situation for
anyone working on it.