On the Firing Line

A military battle is being fought in the 1700's. The best marksmen from both army's have been chosen to be on the firing line and are opposite each other. There are 11 soldiers per side. Initially they are 500 feet apart and start firing at each other. As they march toward each other they stop at a distance 1/2 the initial distance and continue the assault. The marksmen only shoot straight ahead, or range 15 degrees left or right of this line. What is the percent decrease in the potential hit ratio at the halfway mark?