depends on what it's for, I think
for example, a truck route I usually start 2 tiles away from a 'given' city (if there are cities on the map), and usually run them for 10-15 tile widths
for ground attack (tank, troop assault) I try to keep them fairly close, as even our 'long range' artillery ain't so long ranged (for routes that may come up against a 'fortified' position). Infantry is a whole nuther thing ... they move so slowly, and have such short ranged weapons ...
3 tiles total is my usual - the end points for 'start here, and 2 very close together in the middle, so they mix it up.
in the screenie below, I actually have the 'center battle point' in the wrong place, and will need to re write this route. otherwise infantry just sits there, and looking dumb. Tanks will engage each other, but there's not a lot of Japanese armor on Leyte.
(also, for some stupid reason the 'solid ground' is acting like water and rockets and bombs don't go off. something wrong in the HFD methinks. so, this route may be deleted altogether)