When connecting to Thinlinc, users will be redirected to https://</webaccess/login_page>:</webaccess/listen_port>. However, sometimes the correct port is not the one which webaccess is listening on; for example, if there is a web proxy between the client and the ThinLinc server. To support these types of setups, it should be possible to specify a different port for the login page.
If each agent needs its own port, then this sounds like a possible duplicate of bug 3003. If it's just to maintain a symmetry across all machines in the cluster, then we could look at how the native client behaves. It assumes that the same port is used for all machines. So if port 1234 is used for the master, then port 1234 is also used for the agents. Implementing this for Web Access isn't straightforward, though. The port handling is done in the server, which is not aware of which port (or host) the browser used.
As a workaround, perhaps the proxys have some way of remapping the redirection response before passing it back to the browser?
