Be honest...

[FalcoColumbarius]

...Having said that, when there's a rig beside me and one in front, the sudden surge in speed is so overwhelming, it almost brings a tear to my eye.

I find when overtaking a big semi I experience an air wave about two thirds the way passing it. When I initially pull out the driving is quite easy but as I approach the wave I get more resistance but when I get past the wave I get thrown forward (your sudden surge, I suspect), like I've crested the wave and surfing on the forward slope of the wave. One might consider surfing that wave as the optimum drafting position, works for the pigeons and definitely less risky. Only issue here is blocking traffic that wants to get past you. That and the possibility of the semi trailer falling on you, of course.

Falco.

[Morganizer]

Geese do it off to the side (forming V-shaped flocks) so that the wing of the bird ahead parts the air for the bird in behind's body to go through. Makes it much less work, except for the lead bird, and they trade off that role periodically. That's why they don't fly beak-to-bum, because there's greater benefit to passing their body through air that's been disturbed by a wing.