MapSource Pedestrian Routing Behavior Question

[Seldom]

I'm working on a routable map of Northern Arizona.  It includes South Kaibab trail, Bright Angel trail, and North Kaibab trail, connecting North Rim and Grand Canyon Village.  So I've got a reasonably straight pedestrian path from Kanab, UT to Grand Canyon Village.

If I make a route that's less than about 40 miles long from some point on highway 67 to Grand Canyon Village the route takes me down into and across the Canyon.  However, if I increase the travel distance to 50 miles, the route takes me north on 67  to US89Alt, south on US89 and east on AZ64, as if I were hitch hiking.

If anyone can test this behavior on a genuine Garmin routable trail product, or is familiar with this behavior, I'd appreciate hearing from you.

[Seldom]

The behavior described above must be a MapSource peculiarity.  BaseCamp, with a Pedestrian profile routes from Kanab, UT to Tusayan, AZ by crossing the Grand Canyon over the Black Bridge east of Bright Angel Creek, and going up South Kaibab Trail.