Lenses in cameras have multiple elements, which is to say multiple pieces of glass. The front-most piece of glass, or the UV filter one puts over that if they are smart, is the farthest away from the camera sensor and so any flare reflecting off of it will appear to move the most. Any flare reflecting off an element that is very close to the sensor will appear to move less, or even not at all if it is close enough.

It's basic geometry.