On the other hand it is surprising how well full scale pushers perform. As you know Dick Rutan has designed several composite high performance airplanes that all are pushers. There are also many ultra light planes that are pushers. I have never heard that they are less efficient than tractors. Often the opposite is stated.
In the mid forties there was a Swedish fighter that also was a pusher. This fighter had a higher top speed that was calculated. The explanation was that a pusher prop was more efficient than a tractor. Of course this proves nothing. There could have been many other reasons.
All this just as a curiosity. Everything does not work well when scaled down. But it would be interesting to understand why.
/PO