Interestingly, if you have capability to do that, then you might presumably also be able to intercept transmissions targeted at the physical location which forms part of your 4D location. So - the upshot is, there might not be any physical receiving station that we can find in 5C or in Merope, because, although it's there, we can't actually reach it. Unless we're in witchspace...
That's what I would have thought, but as you say if it's in Witchspace we have no way of actually knowing or getting to it. Which makes the puzzle pointless really. It has to be something we can solve, or else what is the point? If the answer is "in witchspace" then they could have just had the Artifacts beaming signals into witchspace, instead of taking us on this long puzzle route that leads nowhere (we can get to). Dunno *shrugs*. I'm just trying to stop the thread going off in complete tangents, other nebulas, other dimensions, when for a long time we've been told it's all about 5c. :/