[CentOS-mirror] How the mirrors work?

Quick question: For some reason, when I do a yum update or yum makecache fast on a newly deployed system our local mirror is almost never selected. It’s very strange because a) It’s a public mirror physically located on campus, so it’s closest and b) the mirror is run on a gigabit connection with a solid state hard drive. Does anyone have any ideas on why our local mirror is almost never choosen as one of the fastest available mirrors?