Steve Hogg has an interesting article a bit related to this, discussing what he calls effective torso length.

https://www.stevehoggbikefitting.com...or-road-bikes/

Keep in mind when you see pictures of a Pro in a very low position odd's are they are pushing on the pedals very hard. That also aids in taking weight off the hands. A position that is comfortable at 400 Watts can be very tiring at 100.