Thanks for the reply Andy - I've managed to control using the curved mix points (channel 49 for x11 etc) but I've had no luck with General Controllers so far - I've no idea why.

I can see how this would be problematic - x amount of keystone rect etc within one mix. It would be good however to be able to remotely switch (via the web server for example) some default param mappers to a keystone rectangle so you could assign the parameters to one rectangle, map it, switch it off then move on to the next one and so on.