When Darris originally designed the prototype of the Sportmaster he sent too Mercury it was only a "2 holer". The "Allison modded" nose has two larger intake holes, one dead center and one port side. The "intake/starboard" side is left smooth for better/smoother waterflow too the prop. Same reason the blowout ring is sometime smoothed on that lower side of the case as well.
:wink
RA