I think so, A-G. Like you, I put mathematics -- though "non-experimental" -- in the first rung because without it you couldn't do any of the sciences occupying the lesser rungs for very long -- and the "harder" the science, the more I think this is true. Mathematics seems to have a kind of divine quality to it that is completely independent of and ulterior to any kind of human "construction." In some mysterious fashion, it seems to indicate the basic form or structure of what is. Epistemology belongs to the last rung, because it has to come in after the fact, as it were, to validate the integrity of any inquiry that claims to be valid or "true" with respect to our universe.
Arguably, mathematics is not a human construction; it is a human discovery. Likewise, I think that epistemology is not a human construction, but a discovery. Both of these discoveries were made in classical and pre-classical Greece. Epistemology as a formalized body is largely the work of Plato and Aristotle. The word itself tells us of its classical origin; episteme is the Greek (Koine) word for "true knowledge." It stands as the opposite of doxa, or "opinion." Its subject matter is the analysis and qualification of what can pass as truth: It constitutes the basic rules for tests of veracity.
First and last and at every point in between, we live in a marvelous universe, a world that is intelligible to us by virtue of these "first" and "last." They indeed (IMHO) constitute the "range of utility of human thought" in its openness to the universe. To try to function outside these bounds is to engage, not "utility," but futility -- from the practical standpoint.
Or so it seems to me, FWIW.
I particularly like the phrase "range of utility of human thought" - range is much better than boundary!
Thank you and hugs!