Welcome to the forum!
Your post is timely. This has been on my mind lately and in searching the forum I found that this has been the topic of a couple of threads.
According to those threads, most of the dust comes out the front of the lower guard. Some members experienced success installing a deflector at this point. I will search the thread and try to post the link.
There is also debate about how wide to set the lower guard. I get best dust collection results with the guard set as wide as possible and I think narrowing the guard (which is necessary to make bevel cuts because of the table tilt) chokes off the dust port and reduces air flow.
I don't know whether you use the DC3300 or some other collector, but I have a DC3300 which can run three hoses simultaneously. I am considering experimenting with a fitting to connect two hoses from the DC3300 simultaneously to the lower guard dust port to try to increase the CFM air flow through the lower guard (although I don't know if that will work of if the two hoses will just compete with each other). I am also considering modifying the upper guard for a dust port (like the Shark Guard). I believe there is a post on here somewhere showing a homemade modification to do just that.
I will be interested in seeing what other responses you get.
Mark V 520, 2 Band Saws (aluminum and cast iron), Jig Saw, Teal Scroll Saw, Belt Sander, Strip Sander (w/chisel sharpening attachment), DC3300, Speed Reducer, Grizzly Jointer, DW735 Planer