The tiny cockpit is a sort of Newey trademark, remember that he’s the one who introduced the fins on the chassis to satisfy dimensional rules.
Ivan Capelli is the commentator for the Italian tv and often he talks about the tiny cockpit of the Newey’s designed March he drove and the pain he felt each time he was at the wheel. Also I remember I’ve seen in a documentary about Senna, a friend of the Brazilian saying : “Ayrton wasn’t happy about that car, he told me at Brazil ’94 : ‘I don’t understand Williams, they spent millions to hire me, the best, and then I’ve to drive half a second slower simply because I can’t fit in the car’”. They also showed AS while entering in the FW16, you could really see the pain on his face.
Anyway I was convinced that with the rules on chassis dimensions/crash tests introduced in the recent years this was no more an issue, apparently there’s still lot of room... for interpretation...
BTW, Barrichello problem wasn’t the cockpit, it was the way they fixed the HANS device, once they adopted the twin safety belts everything went OK, McLaren situation is quite different because they already tried different seats without solving the problem, and the 3rd driver can’t even sit in the car.