Hi Kevin,
I have got a workaround for you. This may not be a perfect solution, but give a try.
Go to your Bex Analyzer-->execute your report-->Right click on your % KF-->Properties-->Sorting-->click on Descending. I tried in my system. It works and shown me % in descending order, which is nothing but ranking in your case.
If this works in Analyzer, we will see how to make it in the Query defintion.
Regards,
Suman