This is a non-answer, but...
When your chin is next to the stem with a flat (or rounded) back, your forearms parallel to the ground, your knees brush the toptube and your elbows are just wider than the knees = you are probably close to best aero, assuming the proper skinsuit/helmet. but the 'grasshopper position' with head hiding behind uptilted forearms on tribars was a thing before UCI squashed it. And Grahman Obree's Superman is position is legendary.
....so (as always) = It Depends.
Most aero without 'most powerful' position may not be the Fastest Position.
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Vintage, modern, e-road. It is a big cycling universe.