Can you get a picture of the buffer tube internal depth? If you are using the spacer, include that when you measure it. 8 - 8.25 inch is not a dimension that I know to work.
As you correctly surmised, Aero is incorrect and a rifle length gas system can definitely function with a carbine buffer system. It just has to be balanced properly. That aside, your buffer is too light. You need a buffer that weighs 5.4 oz or very close to it. At 2.5 inches, your buffer is designed for a standard 7.0 inch buffer tube.
Your recoil system is not correct as far as I can see from the numbers provided. Get some pictures of the measurements and we should be able to get it corrected and functional.
There may be other issues to be addressed, but let's work on this first.