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.