SKU AND title search not working

I have installed your plugin on a dev site and setup a couple of products with a title and an SKU. If I search for just the SKU I get the results I expect:

0847 = 5 results
https://new.letsbuygold.com/?s=0847+&post_type=product&type_aws=true

If I try and narrow down the search and add ‘ruby’ too, which is in the title I expected to see a single product, instead I get far too many.

0847 ruby = numerous
https://new.letsbuygold.com/?s=0847+ruby&post_type=product&type_aws=true

This indicated that the rule on the search is using ‘OR’ rather than ‘AND’? Is there a way to fix this please?

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