I could not believe that the announcers did not mention that it allows a a TD +2 point conversion and a FG to tie. Twelve point lead is much safer than a 11 point lead and a chance for 13. Thirteen point lead buys you very little versus 12. Either 12 or 13 they need 2 TDs. The only way 13 helps is if TB get 2 TDs and miss one or both conversion tries.