Hmm seemed to forget about Des Moines Iowa which is right in the center of Iowa and has distances farther than 7 of these states on the list. Nebraska is 136.1 miles away, Illinois is 230 miles away, Missouri is 184.5 miles away, Minnesota is 103 miles away. Wisconsin and South Dakota are even farther away.
I wish this was a bit longer. Doubt I could list all 50 states in this amount of time, let alone consider their capitals' proximities to their borders.
still, 9/10 isn't bad for a brit