It’s my understanding, and I’m by no means anything close to an expert. When you are running multiple carbs, they aren’t individual carbs, they have to act as 1 carb. And there’s also a reduction in cfm, it’s not a full 1500cfm (there’s some science I don’t understand there.) That’s why the idle circuit has to be reduced by half, and I believe there’s other circuitry that has to be reduced too.