How to select Top/Bottom N results dynamically

I have a relatively simple data set that looks something along the lines of this:

Id      TestName Grade RunTime

Additionally I have two helper tables to use as slicer values for the top N options and to select Top/Bottom.

I have a chart to show the Top/Bottom N tests using their RunTime as value to determine that logic. Additionally I have a dounut chart to show the percentage of grades in all my table. I'm using a way to use measures to be able to dynamically change the TOP/BOTTOM options to see.

TopN Grades by TestName = 
// Var to hold the value of the slicer
VAR SelectedTop = SELECTEDVALUE('Selected Top N'[Top N])

// Assign a rank to all controls based upon total visit count.
VAR RankValue = if(SELECTEDVALUE('Top or Bottom'[Option])=="Top",
RANKX(ALLSELECTED(TestResults[TestName]),[Total Grades Count],,DESC, Dense)<= SelectedTop, // All ranks that are less than or equal to my slicer value are returned.
RANKX(ALLSELECTED(TestResults[TestName]),[Total Grades Count],,ASC, Dense)<= SelectedTop) // All ranks that are less than or equal to my slicer value are returned.

RETURN
SWITCH(TRUE(),
    SelectedTop = 0,[Total Grades Count],
    RankValue,
    // Return all values if Input value is unknown
    [Total Grades Count]
)

When I select the Top option it all sort of works ( I added an extra table to try to debug what is going on):

And when I select the Bottom option my donut chart dissapears:

You can also see that the table I added does not repsect the Top N values selected, it always seems to show more than the selected value of 5 in this example. I can't figure out what I'm doing wrong and I hope someone can guide me in the right direction.  Here is the link to the sample pbix file for this dataset: Sample PBI 

Thanks!