Does does door panel affect the sound?

In many cars, the default speaker location, is behind the plastic door panel. The panel is often an inch away from the speaker, and there is a coarse plastic mesh on the panel to let the sound into the cabin. In many cases, the holes in the door are not even as big as the woofer circumference. E.g., it can look something like this:

http://www.diymobileaudio.com/forum/1099893-post1.html

How does this affect the sound? Does sound sound get lots inside of the panel? Would it make sense to try to cut a round hole in the door panel and install a speaker grille in it? Also would it make sense to install something around the speaker cone to make sure that the sound is guided into the cabin, instead of going into the panel cavity?