I play on an UltraWide 21:9 Monitor, and on Fabrik Der Untoten, the custom perks don't scale accordingly to the width of the gamescreen like the other perks do (see image here: http://i.imgur.com/9tZTmHC.png)

This also kind of happens with the Claymores over on the right side, they are just at a fixed place away from the left hand side of the screen instead of scaling it's placement and size according to the game window's dimensions.