He have issues like that here at the university too, and also got the "it's the *client* that's responsible for roaming decisions".
For instance, I was doing a test at the Library on a private room and my laptop (MB pro) connected to an AP that was behind of another building something like:
My Laptop Library 2nd floor -> 20meters (distance between the buildings) -> another building (2 floors, have others APs) -> 10 meters -> 4th floor AP that my laptop connected. And I was like 5 meters from one of the library's AP. Checked the library AP currently connected users at the time and it had around 40 clients. The AP i was connected had around 20 clients.
It caused some low connections when I was accessing the internet.
We have around 200 zf7962 & zf7363 and now with 9.7 fw version.
We also set, a while ago, with help of Ruckus to avoid clients to connect with 802.11b a.k.a really old wireless cards, we decided to "expand" our area with non wifi signal to guarantee a good quality signal to most of our clients 802.11g/n. But I don't know if this feature stills apply after a lot of FW upgrades. I remember that helps a little with client roaming.