Detection Range of Recon Planes

I was wondering about how far recon planes have a chance to see stealth units.

I was also wondering whether that range is based on where they started/ended the turn or on all the positions it was in during a turn? (ie, should I waypoint a sentry plane each turn to circle an area i want to protect, or should i just leave it at a chokepoint?)

Well for the first part of your question if you click what looks like white circles underneath the mini-map it will show you the visibility range of all your units. As for the second part I'm not entirely sure but I would bet it is only where the unit begins the next turn.

Not 100% sure about the second question but i have noticed visual range changes based off position and the two are related

All detections are happening in the beginning of a turn, at the initial positions of all units. If you move the plane around during the turn, it won't detect anything.