Thank you very much for the proper details and your kind words!
I believe you may have found a bug that I was not aware of. The relevance was indeed not calculated correctly there, it was missing one line in the code. I have done some tests and corrected the mistake on your server directly.
I have also made the following change on your ordering options panel (you can revert it if you want of course): https://i.imgur.com/PXdk7ub.png
The reason is, that using relevance for both primary and secondary does not make any difference, as for items with matching relevance the ordering by ID is automatically used.
Now the relevance will display items that 'exactly match the phrase' then items that 'start with the prase' and then items that 'contain the phrase': https://i.imgur.com/g7Jy3Qb.png
It should give you more expected order as before, in most cases. I hope this helps!
I will of course include this fix in the upcoming release, so you won't have to worry about it.
If you like my products, don't forget to rate them on codecanyon :)