I have one Amsonia hubrichtii growing on the east end of a shrub bed. It gets a bit less sun than yours would since there is also a tree to its south. It doesn't grow as large or quite as thick as the ones that get all day sun, but it seems to be doing fine. It develops color a bit later and a bit more subtly than the full sun ones.
{{gwi:230639}}From June 11, 2013

The more sun the better, for the most part. It's a glade/prairie plant. I've grown in western exposure and it doesn't perform nearly as well as full sun.

Thank you for your help and the photos, beautiful!
I think I will try to find a another spot in full sun...I'm running out of room!