I don't the British issues all that well, but a couple of thoughts I am hoping others may better inform on and I hope OP doesn't object to for going perhaps slightly astray. I have relied on David Luf.tig's (he used to post here before he stopped collecting) article (A copy is here:
https://oldbaseball.com/refs/Ogdens_...ra_David_L.pdf) on the black border Ogden's for them, and he kindly sent me a couple cards that got me collecting these casually. They are a ton of fun.
There are 18 cards in the Heroes of the Ring set. The Leading Athletes also present on this sheet comprise 22 subjects, for a total of 40 in this 'set'.
I'm attaching the old image of this exact same sheet I had in my archive, which is not as good as OP's fresh picture. I think this is from an old public auction but I don't recall the source.
1) If this is a production sheet, 25 small size cards is a very small sheet.
2) With 40 subjects, 25 unique subjects on this sheet is an odd number that would suggest that A) another set of Ogden's was printed in the same run or B) there are probably double print's.
3) If this is a production sheet, we should see poorly centered cards with white borders. I have not found this myself, but again, I only collect these casually and don't monitor every one I can find like I do the N/T/E/C/V.