The intent was that mixes have a one-to-one correspondence to simple cycles. So, examples 1a and 1b induce two mixes, while 1c three mixes.

After thinking over the threat model, I'm tending to agree more with laurentmt's point, and my answer to your question is this:

Combining node-distjoint cycles of the same amount is not only a viable variation, but also has the advantage of larger anonymity size for that mix. Supposing the mix amount is equal, if I were to weigh the pros of a large single trxn versus that of two with a significant time difference, I'd favor the larger trxn.

Threat model: the adversary
(1) has access to the blockchain,
(2) can differentiate, with non-negligible advantage, normal transactions from those that are apart of a mix,
(3) can know the identity of a person in control of an input address of the mix. 

Temporal distance doesn't increase anonymity, because the adversary can still tell which trxns are part of a mix. The larger anonymity set is meaningful, because the adversary can choose to examine only the mix that contains the input address of the person he's investigating. Since that trxn is larger in the combined case, the person is better protected. In the separated case, the adversary just ignores the trxn that doesn't have the address as an input.

laurentmt, this will help in the entropy analysis somewhat. Being that the # of cycles of the same flow amount is also a random variable, the size of the combined cycle is still too a RV.