You lose about .75 for the push rollers.
Also, conditions, you will have to mess with yours to get them right. It is the same (Close) questions when you ask someone what is your dryer setting
Or how long you expose your emulsion.
It depends how deep you blade is set, on the speed, material that you cut. You will have to waste some material, unfortunately, until you dial it in.
Use a few test cuts until you get it close. It will cut triangle inside of the rectangle. If those two shapes weed good, you should be OK.
When cutting, if you have blade marks on the backing (Extensive marks), you blade is too deep (Too far out)
Good luck