Yeah, I think 1 is pretty clearly the option the system presupposes currently. The general idea between the qualitative tiers is just a kind of power that fully dominates some given plurality of things while being irreducible to it, i.e. The power can't be divided down into the plurality so as to be exhausted by it, and the plurality can't be added up to itself (Or to anything else) to match the power. So for example: Low 1-A has no quantitative endpoint at all, you can just go on forever into it, hence a character that has full domain over arbitrarily big Low 1-A realms has a sort of power that can't be equated with any one of these realms nor gauged up as a "sum" of them all, thus resolved into a different sort of infinity altogether (=qualitatively, rather than quantitatively, greater). Likewise a High 1-A character would have power over any and all extensions of 1-A, while not being exhausted by any one of these potential effects.
(To be clear I say the logic holds true regardless of whether the lower tier has a determinate sum or not, hence Tier 0 is superior to High 1-A+, the latter being sort of like the differentiated "expression" of the former, by the same line of thought even as High 1-A+ is supposed to be a completed 'space.' But the indefinitely rising nature of the tiers immediately below 1-A and High 1-A helps illustrate it)
Rating the AP of that as just "Arbitrarily into Low 1-A" or "Arbitrarily into 1-A" doesn't really make sense in my eyes because it's not like their power is indeterminate (Even under a hypothetical where it has no causal influence on its own level of reality). It's an entirely determinate thing that actually, and not just potentially, encompasses and exceeds all possible lower levels (The generative "wellspring" behind all the effects they cause, so to say), which the aforementioned move fails to note, and noting that in their durability section is obviously really awkward, just off the fact that "Attack Potency" is widely viewed as just the explanatory correlative of the "Tier" stat. So the only sensible solution to my mind is modulating the definition of AP a little (At least for these tiers) such that it doesn't include just the external effects that a character dishes out but also the potency those effects emerge from. And this is especially apt given that, from 1-A and up, the "potency" in question generally just identifies itself with the "physiology" (so-to-speak) of the character, save in the odd-case where it's a 3-D character with hax or hax-adjacent amps mimicking a 1-A scope.