org-ql-sparse-tree context

In a literate Org program with each definition being given a heading, and tests being children of these headings with the name "tests", I want to search for headings which contain a child heading called "tests", i.e. find definitions for which tests have been written.

I type `M-x org-ql-sparse-tree RET '(heading "tests") RET`, and it shows me a lot more headings than I want - I see siblings of matched headings, and even other headings with no matching siblings, whereas I'd like to see just the matching headings. According to the README it is affected by `org-show-context-detail`, whose `default` association on my system was `ancestors`. I tried
* setting `tags-tree` to `minimal`
* setting `default` to `minimal`
* `(setq org-show-context-detail '((default . minimal)))`
* running `find-alternate-file` after each of those changes
but saw no change.

Is this a bug? Or am I using org-ql incorrectly? 🤔