In your case as with ANY of the lexan boxes on a 2x4 deal it is NOT the right way. There is a pressure loss in the scoop as air passes the first carb. Keeping the scoop the same size front to rear ensures the rear carb will NOT see the proper amount of air/benefit. There is a reason scoops are tapered in the back, it is an attempt to equalize that pressure difference from to rear. althogh it will NEVER be the same. It is also an issue in a single 4 lexan box but the drop will not be as large since you are not pulling as much air at the front, but there is still a pressure loss to the rear.

In the OP's case he will likely need to make the air pan MUCH smaller than the scoop he has. But in the end to see any benefit is going to require some trial and error. As that scoop opening is WAY to big. But I think with some trial and error he will find a gain it will just take some work to get there.