Eh? Since when was the B series a hemi head?
I do remember reading that BMW did a true hemispherical 4 valve head for a race motor but the valvetrain was pretty complex.
Problem with a hemi head is you have to run a pretty good domed piston to make up for the huge cc’s. But since you can stick big valves in there, the flow numbers are impressive. A good reason why the old Mopar 426 hemi’s were such great circle track motors, though not the best for the street.