Central screw placement is ideal in lateral view , however this is not possible in AP view as there are two screws and one is preferably is inserted close to inferior buttress of neck and other is parallel to it and doesn't necessarily be central. The position however is one of the factors contributing to failure. More noteworthy things are good reduction, well reduced posteromedial calcar region, and thicker and longer nail, no retroversion etc...
For PFN my favourite neck-head screw position is a little below the centre in the AP view and complete centre in the lateral view. Which this position the screw is in better bone quality and less likelihood to has a cutting out.