>In a way, this arrangement resembles a "Buck" transformer,
...except that X1..X2 is flipped over.

It took me a while to get it.

I guess to avoid crossing lines, X1..X2 is turned over in the pictorial view which made the diagram look like the buck transformer with the X1 and X2 terminals transposed.
A "sloppier" picture that retained the X1..X2 orientation would have processed more easily in my brain (so much so that I still feel that the pictorial diagram is not so pictorial).

But the topology of this transformer is distinctly different from boost and buck.
It seems to me that there should be an "induce" transformer to complete the set. It would be like the choke xformer with the primary and secondary swapped. Do you have a design like that?