I look at the "middle", with practice you should be able to see the all the notes you need to play with just peripheral vision. If you're trying to practice your sight reading, one of the things I can't recommend enough is getting good with music theory, if you can quickly recognize scales and chords without having to read note by note it makes it 100x easier to sightread.
another thing, when sightreading you should always be looking forward, when you're playing a bar already be looking at the next bar or two and seeing what notes youre about to play, this gives you the necessary leeway in case there's a wall of notes somewhere.