Thanks so much for your solution. This works well. This is the area where I start to hit a wall in my Tableau knowledge. It seems simple to say "I only want to see the Top X", but then to implement can be crazy. Especially around 'calculate using advanced'.
I still want to be able to understand what exactly all the steps are for so I can implement this and similar things in the future. Do you have the time to go through your instructions in the workbook and explain what each step is doing?
...one other strange thing: I've implemented your solution successfully, but then I add another variable to the 'Level of Detail' shelf and it no longer works. The variable I added was 'App URL' so I can implement it as a hyperlink through the tooltip. Really strange and I can't work out why?