JS2 spec:
Cockpit shoulder width
525 mm

ASH31Mi spec:
Cockpit width
660 mm

Yes, there is a photo of Goudriaan in the cockpit: his position is completely lying down with shoulders under the rims. I don't think you could fly 10 hours in that position IMHO.

When talking about aerodynamic drag the fuselage frontal area is an important factor, especially at high speeds (when induced drag is less).

A pilot must take a decision: top performance or compromise & comfort ? Both is simply impossible.

(This was a factor when I had to choose between ASH31Mi and Ventus2CxM)