By Jove I think you've got it!
I was looking through my service manual & Clymer last night to try to find a definitive answer for you and some other guys and could find no other
specifics on head gaskets other than the "fold" of the steel ring in a composite gasket. As yours is stamped steel it does not apply.
Larry makes an excellent point. If the larger holes in the water jacket were inline with the supply side of the pump, you would have little circulation around the other side of the head as water
(like electricity) will take the path of least resistance.
Restricting the supply side of the cyl head will force water around to the left side of the cyl and then through the larger hole in the gasket up through the head.
( If this just makes things more confusing I'll come back and delete the post as irrelevant.)
Tuck\o/