Odd question about tires

I found out where my MPH and ET went! My ET Streets measure 27 1/2 at 18lbs of air and my old Sportsmans measure 26 inches tall at 18lbs of air! The funny thing is both ties are listed at 28 inches tall! I gained 1 1/2 inches of gear killing tire...thats why I was trapping almost 400 rpm less with the tire change.