In my opinion, each tier (and sub-tier) should both have its own established identity and expect to see some reasonable degree of use, as far the two can be negotiated with each other, and up to now I think @Agnaa's iteration of Option 1 accomplishes this the best:
"1-C", on the whole, has the clear task of sorting out characters who transcend normal reality by some tangible number of higher realities. This is further sorted nicely into 6-11-dimensional for Low (a contingent with boundaries clearly established through existing scientific theory, and that makes sense based on the general frequency with which such tiers appear), 12-to-transfinite for Mid (which again should see some use, and catches everything Low before it or High coming up does not), and then High 1-C for "infinite-Dimensional" as we understand it currently: this recurs frequently enough here, and is noteworthy enough as a classification, I find, to warrant its own rating.
1-B's job is likewise to sort out the characters that transcend "transcend normal reality by some tangible number of higher realities" here, whether only by a relatively minor margin (Low 1-B), ordinarily (normal 1-B, for baseline), or extraordinarily (High 1-B.)
If we wanted to keep the Tiering System mostly the same, and simply expand what ranges of 1-A exist, we'd need to ask ourselves what functions those classifications serve to fulfill. It's one thing to say "something is better", and another to consider why it's better (or not) in the first place.