When placing food items in my sous vide bath, often the pouches will rest on the bottom of the bath or against the sides of the container.
I've also seen dedicated sous vide magnets used for attaching items to the side of the bath that prevent the bags from floating. This will press the bag even closer to the sides of the bath.
I would assume that even worse case, conduction through the food itself would bring the item up to temperature. On that basis I generally leave food in at least 30-60 minutes over time to compensate for this when a bag is very close to the side or resting on the bottom.
Is it essential then that any food cooked sous vide is totally surrounded by water? If so, by how much? 1mm? 1cm? 10cm?