While I do prefer to not be sitting just inside the door with my back to it, I otherwise place no particular importance to where I might be sitting in a restaurant. There's always the possibility of "X". I simply choose to ignore a lot of those possibilities. So does everyone else.
Well... everyone else may choose to ignore it but not me.
Although I don't obsess over it or let it ruin my day, I always try to be aware of my surroundings. It's good practice for CCW as well.