They probably work better as far as flame travel if you think about what happens in the chamber as soon as the spark plug fires. Closed chambers only cover half the piston and the explosion starts pushing on that half of the piston for a fraction of a second. Flat top motors with open chamber heads usually run good.
Also valve shrouding..... My 318's with the factory open chamber heads have always pulled harder in the rpms than the 318's with 302 heads (closed chamber). Just my experience.
