Let a base, relay and 3 nodes run most of the day while counting the traffic:
XMIT: 47D7, ACKS = 3839, NACKS = 696, XMITS = 4754, RETRIES = 3979
SENT 47D7
ACK: 47D7
XMIT: 45A7, ACKS = 3840, NACKS = 696, XMITS = 4755, RETRIES = 3979
FAILED TO SEND 45A7
SENT 45A7
ACK: 45A7
XMIT: 8BDB, ACKS = 3841, NACKS = 696, XMITS = 4756, RETRIES = 3980
FAILED TO SEND 8BDB
FAILED TO SEND 8BDB
SENT 8BDB
ACK: 8BDB
"RETRIES" indicates a radio.write() that returned false and was retried (usually it retries several times)
"XMITS" are radio.write() that returned true
"ACKS" are received acknowledgements
The good news is most messages get through. The bad news is it takes lots of trying to get there. For my planned purposes, I don't see this being detrimental. I would only need to send a message at intervals of several minutes. So retrying several times won't matter. And if I have to send out twice as many and just throw out the extras to be sure they get received, I'm OK with that.
I really should try to count the receptions at the base to find out whether ACKS are missed because they were not sent back from the base or were simply not heard by the node for some reason.
I just hope the success rate doesn't fall off rapidly as the number of nodes increases. I still have to prepare 6 more nodes and possibly another relay depending on what I find in actual operation. I will get that question answered once I have them running.