UltraVNC embedded with proxy

I'm using ultravnc's repeater proxy, but can't seem to get it working with an embedded tab.
I can get it to work externally using command line arguments field "/proxy 192.168.13.205:5901"
I have tried both the optional parameters field, and the Proxy field for embedded, but it simply fails, and doesn't seem to attempt a connection to proxy.
Is there something I have overlooked?
Thanks