All other things being equal wheelbase has a lot to do with comfort and stability. The Brompton's wheel base is by far longer and is actually longer than the average hybrid bike. Throw on some bar ends to an S stem and you will probably feel less cramped than the Dahon. AFIK, as the Brompton was designed for commuting on crowded streets with a lot of cars, the M and H bars were designed to give the rider an upright position to aid in navigating traffic. If you find you are still too bent over you can use riser bars with bar ends.