As long as the question is about the venturi and airflow around it then this forum isn't a bad place to discuss it. But let's mostly confine the discussion to this aspect.

Something to consider is that short mouths on carbs of any sort do odd things when air flows past them. And when you add a cowl near to the intake the issues compound greatly. Remember the old 60's muscle cars? Many of them had hood scoops. Then some bright wig got the idea of raising the opening on a standoff so that the "turbulent boundry layer" along the hood was not the source for air but the supposedly smooth flow about an inch and a half above the hood. Then another bright wig actually did some tunnel testing and found that even BETTER boost could be hand by having the hood scoop turned around so it could draw air from the high pressure zone at the base of the windshield. Something that was completely counter intuitive to many of the folks out there that lacked the understanding to know why the darn hood scoop was mounted on backwards!

Then there's the opening turbulence issues. The aerodynamics of the carb opening on most carbs is not all that clean. Adding a velocity stack venturi may help this and with some tuning you may find that it may make the engine run more smoothly. Even in my motorcycles if I open up the airbox over the 4 carbs there's short venturis inside the airbox. The function of these being to smoothen the air "stack" being drawn into the injector bodies or carbs. Otherwise the air tends to be drawn in from the sides as well as the front. And when it passes over the fairly abrupt lip of the typical model engine carb there's going to be some turbulence that tends to "jam up" the opening. The idea of a properly shaped venturi is that the flared lip acts a bit like an airfoil's leading edge to smoothly bend the air over the nose of the airfoil without creating any separation. The function of the venturi is the same but it smoothens the sideways inflow of the air by smoothly bending it down so it lines up with the direct center column.

Play with it if you want. Adding a nicely flared out venturi to the mouth of the carb may allow it to run more evenly at full throttle. Or depending on lots of issues you may not notice a difference at all.