Looking back at the two pictures you included................

There is a somewhat square bulge in your lower cowling. I assume that's where the muffler will be. The front of that bulge will work as a deflector. If you remove cowling behind that, the resulting opening should be in negative pressure.

Don't go crazy making the opening look huge from the bottom view. The area that matters is basically "frontal area" since the intake openings are "frontal". To speak "geometrically" (like we had to in Geometry class), the plane of the intake opening is the plane on which you'd measure the intake area. The exhaust area has to be figured on that same plane, only further back where that opening is.