[71T Targa]

I've been looking at red dot sights and I can't seem to get my head around how they work.

Does my eye/head need to be in the same place every time? It seemed like I the dot moved depending on how I looked through the sight.
With iron sights you have three points in a line, rear sight, front sight, and target. You eye must be on this line. With the dot you only have two points, and your eye can be off-line.

I just don't get it...