Take a look at the design of the air box, itself, and how the filter fits, and how air flows through the filter, to the carbs. You should see that air flows from the back side, beneath the seat. You should also see that the air flow won't matter which direction it comes from, as the filter is oval shaped. The plate did not have louvers in it, from the factory; if you add louvers, it will not affect the air flow, except to possibly add a small amount of additional air flow -- not enough to matter. It will be easier to make a solid plate, but if you want to take the trouble to add louvers, go ahead. Cheers!
1979 CB750K (sold, 2012, but not forgotten)
1983 Kawasaki 440 LTD Belt Drive (sold, 2011)
1993 Kawasaki Voyager XII