Word document results missing default HitHighlightedSummary on search page

SP 2013 on-prem. We are site collection owners so can’t change or look at anything in central search services.

We are just standing up a site with a custom results page. Some of the results are documents like Word and PowerPoint files.

If I search on “word OR PPT” I get a powerpoint file and a word file. Neither file contains either ppt nor word as part of the hit highlighting summary. The ppt result shows a “default” summary that includes just a bit of text extracted from some part of the document. But the word result doesn’t include any summary text and it makes the result look weird.

I used my browser debugger to put breakpoints in the item_word.js and item_powerpoint.js item rendering templates. At both of those places I check the value of ctx.CurrentItem.HitHighlightedSummary. The ppt result had a value, but the word result didn’t.

If I change my search to search on something that is included in the body of the word doc, in this example the word “change,” then I do get a regular hit highlighting summary for the same item’s result.

Is there somewhere that the default value for the summary comes from if the actual search term isn’t actually able to be highlighted?