Pivot to Filter Bottom % of Ranked # ROWS not Values

Hello $Kas29 and Welcome to Excel Forum.
Perhaps this will be of some help.
Using the filter/sort drop down arrow in cell C3 select Values Filters > Top 10 > Show Bottom 6 Items by Rank
To have Excel determine the highlighted number:
1. In cell K1 place the percentage of rows to be displayed
2. In cell K2 display the number of rows using: =INT(COUNT(D:D)*K1)
Note that points 1 and 2 will not automate filtering in the pivot table, they only aid in figuring out how may rows to display.
Note that when you open the attachment cell K2 will display 1 because filtering has already been applied.
Let us know if you have any questions.