Found the answer!
On the router (routers if you have more than one):
Enable JV 
Make sure you save it, the Pencil icon in XCTU
Power up the coordinator 1st,
Power up the router after, making sure they are not too close to each other.
I read: Coordinator Operation: ...Channels with excessive energy levels are removed from its list of potential channels to start on...
I guessing, what's probably happening is that one starts developing ones code/system with the two units on the table, and the channels selected are far apart due to the above routine. If JV is not enabled, they stay that way, hence, range issues.
Please correct me if I am wrong, or missing another step which would make this process a bit more user friendly??
Many thanks ...