Look at how closely race cars and cyclist follow each others tails to benefit from drafting.
Geese coordinate the way that they flap their wings to maximize the benefits of each others slipstreams.
Important point is that the second aircraft is not "drafting" You're not getting a tow.
The second aircraft is surfing the wave out to the side of the first. It's similar to the Kelvin wake. visible here
https://upload.wikimedia.org/wikiped...-_DSC06962.JPG
And if you're surfing the wave, you're getting free uplift, so power reduces.
At least that's my recollection of discussion with some researchers in the early days of this project