http://www.squaremans.com/images/Urland01.jpg
That map should illustrate the problem. At the top, big forest. Looks good. Large symbols, densely packed together.
Then in the middle is a smaller forest, using the same tool, but note all the white space. My expectation is the white space would be filled with trees, a la the larger forest above. I think I've successfully scaled the symbols in the fill, but not the rate at which it draws them. So both forests have the same density, but since the forest in the middle has smaller trees, there's more white space.
Symbol Fill doesn't seem to do anything, when I monkey with stuff like X and Y spacing using the Deciduous Fill, which it says is currently selected, all that happens is I get a green background under my forest when I draw it, and I think the green background green trees, not part of this map style. Here's the Symbol Fill box.
http://www.squaremans.com/images/Urland05.jpg
When I select Terrain Fill, I can bring up the Advanced Options and this is what I get.