Can I create multiple grade rates within a business group?

My customer has the requirement to benchmark at position level. I had hoped that I could create a grade rate per position, link the grade rate to the relevant grade and the minimum and maximum salary for that position (we have one valid grade per position) then link the grade rate to the position. Unfortunately, I have tried this and it is not working as expected. The salary range and related data (quartile, median, etc) only displays when I have one grade rate. As soon as I create a 2nd grade rate for another position, the 1st one still works but nothing pulls