It's not just "endless" or "infinite" but there are an inaccessible amount of layers between H1-A and 0 as there are between 1-A and H1-A.
First, let's start with this explanation: Transcending H1-A qualitatively or seeing it as a fiction will give you 1 layer in H1-A, just as you gain 1 layer in 1-A, and you can make it even larger. For example, imagine a hierarchy, there are infinite layers in this hierarchy and At the bottom of the hierarchy there is a H1-A place, in this hierarchy the places are stacked on top of each other and each place transcending the other qualitatively or sees it as a fiction. This hierarchy will take you to the infinite layer in H1-A. To go beyond this and transcending this hierarchy is not enough for tier 0, it just puts you on a higher layer in H1-A, all you have to do is be inaccessible to this hierarchy for tier 0.
Another explanation of layers would be:
Well, on the wiki you can still use the power sets to transcend layers at H1-A or 0, Which means you can say that
0-innaccessible is baseline H1-A, P(0-innaccessible) is 1 layer in H1-A and P(P(0-innaccessible)) is 2 layers in H1-A, If you repeat this power set operation infinite times, you can go to the infinite layer in H1-A, but as in 1-A and H1-A, it is not enough just transcend infinite layer to reach tier 0.
For tier 0 you have to transcend this whole 0-innaccessible hierarchy in an inaccessible way. To explain this better, if you define λ as a cardinal in any 0-innaccessible hierarchy, whenever we have λ<κ there is 2^λ < κ, so here no matter how big you make λ, it will still be smaller than κ.