Kunai,
Don't know if we answered your question and some of us aren't really sure what the question is! The ratio of the full frame sensor or film negative or slide, is more 2x3,so a 4" x 6" print is the uncropped image. An 8x10" print, is a bit squarer and part of the image will be cropped. Here's an example: If you go to a Lab and order a full frame print and say a 16x20", they will take the longest side,20" and then print that. The paper itself will still be 16x20, but the image will be closer to 13"x20" on that paper. If you go to the same lab and order a 16x20,boderless,say,they will need to know where you want your image cropped, or they'll crop it for you.
For FAA, if you want an image, JUST THE WAY YOU WANT IT, then upload that cropped image and you're done.
Most frame sizes and mats, are designed for cropped images,5x7, 8x10,11x14,16x20 etc.,so a full frame image on a print,with one side 8", the other side will be closer to 12", or an 8x12.
So any combination of "2x3" will and can give you a full uncropped print,from a 35mm DSLR,
Rich