Maybe I don't get it right, but just want to sort by ascending / descending # of Yes and No?
Try this ... Go to the answertext heading and right-click, then go to the interactive sorting tab in the properties.
Select "Groups" instead of "Details" (radial button). In the sort by: field, select the response text group. In the last section, where it says: apply this sorting to all groups and regions of data in: Select the entire / tablix matrix. Not positive, but I had a matrix, and the last step was the key to sorting it ... in details or groupings, etc., Sorting only works if you apply it to the entire tab.
source share