The last time I researched this, it would be: "or is this just from the top tier to the next level K-1 owner?"

Your scenario: US LLC owns the FDE(s), and each FDE uses Form 8858 to report to/for the LLC (considered the only real entity in this flow). The LLC is its own entity. The S Corp not only also is its own entity, but I seem to remember S Corp and REIT (what I was researching) are excluded from filing Form 8858 anyway.

And I remember 10% being the minimum for "US persons who operate an FB or own an FDE directly, or, in certain circumstances, indirectly or constructively, are required to file the form." That would be the LLC, anyway. Not the 1120-S entity nor the 1040 entity.