Overpressures in the sonic boom impact area, however, will not be uniform. Boom intensity is greatest directly under the flight path, progressively weakening with greater horizontal distance away from the aircraft flight track. Ground width of the boom exposure area is approximately one statute mile for each 1,000 feet of altitude (5 m/m); that is, an aircraft flying supersonic at 30,000 feet will create a lateral boom spread of about 30 miles, or at 10,000 meters a spread of 50 kilometers.Other maneuvers, such as deceleration and climbing, can reduce the strength of the shock. In some instances weather conditions can distort sonic booms.[4]
However, not all booms are heard at ground level. The speed of sound at any altitude is a function of air temperature. A decrease or increase in temperature results in a corresponding decrease or increase in sound speed. Under standard atmospheric conditions, air temperature decreases with increased altitude.
A vertically rising missile doesn't create a "carpet effect" of the sonic boom traveling across the ground the way an aircraft does because it is not traveling horizontal to the ground. The cone of the boom is all straight down from it. In order for the boom from a missile to be heard 35 miles from its launch point it would have to be over 30,000 ft in altitude as said above. Obviously a missile would reach supersonic speed long before it attained 30k ft. The other factors mentioned above explain why it would carry even less of a distance. Has anyone watching a shuttle launch from the Cape ever heard a sonic boom from the shuttle? Of course not.
I wonder if the word ballistic (the B in ICBM), might be informative here.