Start 25, IPhone app and online planner show different routes

rullfarm

Hi. My phone app and online route planner show the same route and the one I would prefer. My Start25 shows a different route and one that includes narrow lanes (previous experience otherwise I wouldn't have known). Why is this? I'm hoping I've managed to put a waypoint in on the Start 25 to direct me on the better route but is there a way of avoiding this problem in future?
Thanks
Sally