Though it isn't exactly the same, this reminds me of our discussion back in Aug/Sep about Corn and Maize, much of which is on Phabricator: https://phabricator.wikimedia.org/T110571 .
The behavior you want happens sometimes. Searching for "usually" gives as the first result: Convention (norm) (redirect from Usually)
"difficult": Difficulty (redirect from Difficult)
"corn", among its many odd behaviors, gives: Maize (redirect from Maize corn).
I think there's some sort of ranking going on for redirects that can put a partial match above an exact match (hence "Maize corn" instead of "corn" as the redirect shown).
More relevant to your example, I think that if there's a match on one or more search terms in the redirected-to title, it blocks redirected-from titles from being shown. Searching for "neropathic" gets a spelling correction to "neuropathic", which gives as the first result: Peripheral neuropathy (redirect from Neuropathic).
David may know more about either of these cases off the top of his head. (But maybe not, since it was a while ago, and I recall that it was very messy, and we declined to work on it then.)
So, at the very least, the control group would at least sometimes have a chance of getting the test behavior because we do that now under certain circumstances.
Another option is to consider this a bug fix so that we have consistent behavior whenever there's an exact match of the query to a redirect title, regardless of partial matches to the redirected-to title or higher-ranked redirects.
It would also be interesting to know how often queries get redirected results, and how often they show the redirects—either in general, or as part of any A/B test.
—Trey