What you describe does not work for me. You can use the absolute size to set a preset, but when you go to use that preset it does not function as you would expect. Absolute size is functioning more like a resizing mechanism that uses ratios and re-samples your image. This thread talks about it a bit.
An example with a random image I pulled from the internet: I want this to be 1348px x 821px, so I set up a preset for that. Using unconstrained the image crop should be at this size:
When I go to the image and select the preset, this is the bounding box that actually shows up on my screen:
Thanks for looking into it, but your method is not working for my version for some reason. (I'm using 1.7.1)