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here is my definition utilizing my etymological knowledge (I study much more than nature):

a lower (kat- [down] + episternum) lateral division of the thorax
as opposed to the proximate upper (an-) episternal division of the thorax

katepisternum (adjective=katepisternal, id est, katepisternal seta[-e])
sternopleuron (adjective=sternopleural, id est, sternopleural seta[-e])

the term sternopleuron is used in most German text instead.

https://diptera.info/infusions/terms/terms.php?op=view&id=309

unfortunately, the katepisternum is not viewable in any of your additional photos.
https://insektenfotos.de/forum/index.php?page=Thread&threadID=89046

a lateral view is necessary and sometimes from below.