I run a website for a fine artist and first of all this plugin is great! I use it to display thumbnails of his artwork in retina quality and I love the results.
With one of my custom sized portfolio thumbnails I used another plugin to re-crop the image. Unfortunately the retina version isn't cropped the same way. I think I have no chance to access the x2 image with the other plugin to get the right image section on display.
So I guess the only chance is to manually upload a cropped version and name it with "@2x". Or am I missing something?