The SharePoint project I'm currently working on uses a custom search results page. We've customized the display templates, the search results webpart, and the refinement panel.
An enhancement to our system calls for the number of refiners to be increased from 19, to 21. In the refinement configuration I was informed that "For performance reasons it is not allowed to select more than 20 refiners." and the option to add more refiners is disabled. I wasn't aware of this, I couldn't find the answer on the net or from tinkering with the webpart, and it seems to be a hard limit. Up to this point the message was "Selecting more than 10 refiners can degrade search performance" but the performance of the search has been more than adequate with 19 refiners.
How can we break this limit of 20 refiners in SharePoint 2013 search?