If I'm to provide a UI to this filter, I guess it would fall in the Effects category
Personally I never open the Effects panel and I wonder how many users are familiar with that panel. So I would not serach it there.
I thought that the Effects panel was for the slides!
For me there is only one place were you should place this, in the panel where you define the thumbnails dimensions. In my own skin I have these two options now on a thumbnails tab.