I mean, I found tons of good spots for Dunsparce. Not because I found places where he could really cover the track, but because he only needs an enemy in line of sight once every few seconds. Upgrading him made his range so huge that he could get planted in the center of the map and almost always have something to target.
Just don't worry about having an enemy in los all the time. Worry about there being an enemy in los when needed and cross areas work a lot better