Thanks!
I see the issue now. Basically, when using the index table engine, there is a two phase search/ordering, and on phase one relevance is still considered, and then the matches are reordered twice by the primary and secondary ordering.
In this case the most relevant matches to the keyword were picked up to the limit (10 results) and then reordered by the algorithm. To make sure there is a wider range, I resolved this by increasing the live results count to 50 here: https://i.imgur.com/M1vF6wv.png
This will leave a bit more room to match and order and should resolve the issue.
Another possibility is to use the regular engine and revert back the results count to 10. The regular engine will disregard the relevance completely for the matching if the primary ordering is not set to relevance – so will return any matches by the date prioritized.