pl attach a workbook to help you.
I apologize, I am current not allowed to send workbooks. Were you able to see the screen shots?
If so, I can sent the actual calculated field formula and parameter, and I can send a pic of the worksheet feeding the dashboard.
The problem is that you are sorting by an individual field. Changing the parameter selection doesn't change this field. So, the sorting works only for the original field. You can rectify this by creating a new calculated field which will incorporate both total percent and count of grade. I don't know how your data is structured or the names of your fields. So, I'll only provide a general form of the code which you can adjust to suit your requirement.
IF [Parameter] = 'Show by Percent' THEN [Total Percent]
ELSEIF [Parameter] = 'Show by Count' THEN [Grade Count]
Then use this calculated field for sorting.
Hope this helps.