We have added 3 new Show Value as options.  Now you can show value as a percentage of a parent. There are three new options, % of Parent total, Parent column total, or Parent row total.   

Parent total lets you choose which dimension or grouped dimension's total to use as the parent, while the row and column totals use the location of the dimension within the pivot to define the parent.

Test it out or read our documentation if it's not apparent.