Answer: Topping them will only serve to make them flat on the top. To promote a denser, more bushy plant, you can shear just a few inches off the plant all the way around and from top to bottom. Pruning encourages additional growth and shearing just a few inches from the tips of the branches should force growth inside the plant near the trunk as well as at the site of pruning.
Best wishes with your landscape!
Q&A Library Searching Tips