My Sukkan Sugi gets a fair bit of shade from a fence, nearby shrubs, and a neighbor's large ash tree. I'd say it gets around 4 hours of direct sun and an additional 4 hours of filtered sun. I chose this cultivar partly because it was supposed to be shade tolerant. I read somewhere that they fill out as they mature, but you're probably right in that the lack of sun is probably to blame for mine looking somewhat thin.
Take a look at this hedge of Leyland cypress. 130 FEET and still growing!
http://www.bbc.com/news/magazi...
I can't remember if I've shared that link before, but it's hilarious! Make sure to watch that video. And the naked man!
British homeowners hate this tree because they get so big (especially in their climate), and they have such tiny gardens to begin with. It's interesting how the person on the video says it's not a weak tree. That's because they don't get our winters!
