Re: Gamma Suggestion. The Problem.
Sundial: I think just restricting the distance you can place terminal to the teleport is enough. Say the circle has 2km radius, you can't place terminal closer than 4km to tele.
As for restricting distance between terminals: I don't think that would be needed. The closer you put terminals to eachother, the less you have safe area, if someone wants to go that route, let him.