Fans are the largest part by far.Presence of fans is PART of the home field advantage. Travel is another part. Playing in the most populous city in the home state of a rival university to me confers an advantage. Maybe I’m just jaded after seeing Illinois get screwed in the past. How about playing the sugar bowl against LSU in New Orleans or the Rose Bowl against USC in Pasadena?
I can't believe you're even mentioning those football venues. Do you realize we had nowhere close to 40% of the crowd in any of the major bowl games we've played in.