I think you're well on the way to achieving your goal.
Yes, the shorter treetops help, and I like what you did with the vertical hatching across the rest of the forest but I'm finding it a little hard to look at.
I took the liberty of dragging your latest update into photoshop and playing with things really quickly... one version just added a rough ground shadow, the other I used a clone stamp tool to pick up some of the treetops and scatter them over the canopy. Just for your consideration. It may not be what you want to go with or it may inspire something.

pine forest shading ideas.jpg