One detail that's seldom mentioned about pushers.............

When the fan is close to the wing's trailing edge, there will be an unsolvable problem.  The size of the problem depends on lots of things, but it's one reason there aren't a lot of commercially viable pushers.   The air the fan see's over the top of the wing versus the bottom is different.   Different pressure, turbulence, lots of differences.   Depending on all that stuff, and it's impact, it's often less efficient.   Sometimes it causes additional problems, like odd vibrations.