Don't know if you are aware Bazz, but Gary Tempest learnt that someone had X-Rayed a faulty Wellbrook loop antenna and had reverse engineered it, referring to it as the 'Wellgood loop'. Gary decided to carry out further experiments after his successful initial design, which resulted in a 'MK2' version, which has the merit of being simplified, yet with enhanced performance.
The updated design featured in the Spring 2018 BVWS Bulletin.
(It's on my round tuit list!).
Unfortunately, Gary isn't a member of this forum, but wrote about his updated design at post No 11 in the thread at the link below. He also owns a Wellbrook loop so was able to make comparisons with both his earlier design and the Wellbrook. His views on the performance of the second version on the short-wave broadcast bands were favourable:
https://golbornevintageradio.co.uk/f...id=5944&page=2
This doesn't of course answer your query, but nevertheless, I thought it might be of interest.