They only got 110 pounds up there, not nearly enough for a nuke that’ll pump out enough EMP to do anything. And they’re still about 14 miles short, which doesn’t seem like a lot, but distances straight up are a lot bigger than they sound.
14 miles is irrelevant, even if it only impacted half the US the damage would be massive.
the payload size is important but you’re assuming they can’t increase the payload size.
Don’t forget Iran is building launch sites down in South America (thanks Chavez) which would place the eastern half of the US in range of a non-orbital payload.