You are thinking it is most efficient to run the windmills without obstructions. Obstructions basically let you set the max safe height to run the windmill. The fewer obstruction you have the lower you can run the windmill, but the more spread out the windmills need to be. So the higher up you go the more compact your windfarm can be.
If you make a layout with no obstructions you might have a spiderweb of windmills spaced 8 blocks apart and do it at height 80 or whatever height actually has no chance for 0 obstruction windmill to break in a thunderstorm. Wind done with 0 obstructions ends up spending more resources on wiring the farm than energy production.
If you go up higher instead of a web of wind mills you can now stack them in a column like a water mill and use the obstruction of the others to keep all of them running at a safe EU/t. Each windmill still roughly outputs the same power as an ideal no obstruction windmill at height 80 (or whatever it is).
The most efficient layout then becomes the one that packs the most windmills in the smallest space, no? A column of 64 windmills, 16 high (4 sides around a tin pole), starting at ~190 can be safe with just the windmills and some extra blocks on the top. And the next windmill tower can be 4 blocks away. There are newer design that pack them in even higher and tighter.
Edit:
That being said i would not do wind again
Ugly and working at max height is annoying.