Hi Matt,
Could it be this one:
https://www.google.com.au/search?q=W...UTF-8&hl=en-au
Seems the name is P-FLAT68, but on some photos looks different. Maybe the cone shaped part is added separately?
As per
https://www.astroshop.eu/field-flatt...-series/p,5034, Lens-to-chip suggested distance: 68mm.
But then, there is this link
https://www.opticsplanet.com/william...e-flat-68.html to this diagram suggesting what it looks like different distance:
https://op2.0ps.us/static/lib/supple...ChiptoLens.gif, 46.45mm with the cone adapter, else total distance 113.13mm.
Confusing…
Another link I found,
http://www.astro-photography.net/FLT...e-problem.html, but seems this person doesn’t use the cone adapter, so he had to add distance to get it it to the recommended total distance of 113.13mm
Might be a matter of playing with the distances and see if any of them works.