Moving next to the aTV shouldn't affect it
when using wi-fi all devices connect to your router, and not directly to each other (so signal goes laptop->router->aTV)
so it's probably that you're moving your laptop closer to the router
**although, with the kind of new peer-to-peer airplay, it might be doing some magic in the background and connecting wi-fi directly.
with current hardware, screen mirroring will have quality issues,
it can't encode the image until it appears on your screen.
there's then a trade off between keeping the images on both screens in sync and quality of the image.
Other options (like
beamer) have the ability to read ahead in a video file, and build up a little buffer to handle network issues. and result in a much better image on the aTV.