Just a guess: the Zenith covers all starting, idle and part throttle cruising with the smallest venturi for best response and mileage.
The 3 X 1 in the original ports provides WOT power without the concern of bad distribution due to progressive linkage.
Years ago an XO LSR team tried to modify a Buick L8 using the same technique (extra port supplying the siamese bowl and valve) and were given permission. When the car turned out to be fast, they said it's illegal. Very disappointing.
