How come the advertised upload speeds on the plans are significantly higher than what I am receiving at my home?

I pay for the plan advertising 1100 download speed with typical uploads of 300 - I am getting 42 connected via ethernet. I have had 2 techs come out and they have come to the conclusion that xfinity is limiting what I am receiving because the incoming signal is 400. My equipment has been checked, cables, and the second tech even called xfinity support who told him in front of me that my plan was 1100 download with 35 upload. But I know what I signed and I know what I was under the impression I was signing for as I did it in store with a reps assistance.