As far as flying is concerned ,generally, the closer the better.On the other hand, you do not want the two leadouts to interfere with each other , or snag on each other.In the NORTH WEST many good experienced flyers stagger the leadouts from 4" to 6".(One is longer than the other).The downside is that you must make up your lines staggered also. I have for many years used a 6" stagger , and I separate the leadouts 3/4" to 7/8" at the tip. Never a problem.
On the other hand I fly with many fine folks that use two individual leadouts , so the gap can be changed at will. Keith Varley