Pixel mapping/Artnet Merge help

I’m hoping someone can help with some issues i’m having with Artnet merge.

I’ve got artnet coming in from Resolume on Universe 4 and I can see the incoming data in the DMX Input window. I’ve got it set to HTP merge with Universe 2 where I have my fixtures patched but I can’t see anything going out in the DMX Output window. If I setup and enable some channels in the Mapping tab however it does work. My understanding is that you shouldn’t have to do this however when i’ve got a 1:1 patch from Resolume to Onyx