Hi Kris,
I have found that it takes a lot of trial and error to get AI to go where you want it to go to, short distances seem to work quite well but for longer distances I have found that the only way to progress is to set up the AI, run the mission, see how it looks and then tweak by moving start points/endpoints and run again - it takes a lot of patience and do not make too many changes each time otherwise you will get completely confused. By doing this I almost have two very long missions with loads of AI all going where I want it to, but have been working on and off on them for weeks, and still not completely happy with them - but, it is a great feeling when you run the mission and finally the AI looks close to what you had hoped it to be, don't give up :-)
regards,
Andy