Could a smaller plane fly in a V formation behind a much larger plane to reduce fuel consumption significantly more than a plane its own size? At what point does flying in a larger planes wake become to turbulent or increased fuel efficiency stops?
No, airplane wakes do not work like this. The streamlined body has very little wake, it is not like a cube shaped truck. The main wake on an airplane is found at the wingtips in the form of a strong vortex like horizontal tornado, aided somewhat by the down wash of the mid wingspan.
The tip vortex from a large plane will make a small plane spin like a windmill. A german bombardier challanger(mid size business jet) flew under an A380 at cruise altitude a few years ago and was turned over so hard the plane had to be sold for scrap, broke a one passanger's ribs, recorded near 4G force, lost 8000 ft of altitude before recovering control.