Thanks for the reply.
I have resolved my initial problem - finding the LED driver card settings has given me the exact panel sizes and XY positions. Everything is now looking good.
However, I still have an issue with the output on two of the panels.
I've been trying to work this out for myself and I think it is down to how the LED driver card was initially set up.
There are two LED panels which are both physically 16x640 each. The card settings show them as a 32x320 and a 64x320. So, presumably this is why the physical output looks like four panels of 16x320.
I want it to show as two panels of 16x640. So, is it simply a case of just changing the card settings or is there a reason that it was originally set up like this?
Also, is there a way of setting up a "send to all" layer that overrides all existing layers and then returns them back again - like a mask?