Jib leads

I am re-rigging Douglas hull 2144 and have a question about the position of the jid lead tracks. The handbook says the track shall be no less than 15" from front of cockpit. The original track on this boat is closer to 16". Is this measurement critical to obtain best jib shape? Should I move the lead to max forward position? The track is quite long. How short can I make it to get full adjustment for different wind levels.I am thinking 8" should be enough. Thanks Joe