Let's not gloss over what MB said.
He said 'the message has a very specific purpose and it's very different from the UA'.
Do we even know what the purpose of the UA or the morse they broadcast is? We don't.
We have a very strange rule to follow in our hands. Speculate a theory for the UA and something distinctly different for the UP.
This is like solving two equations with two unknown variables. We can see the results, we have to figure out the variables.
I think there are much more than two unknown variables! But a bit of intelligent speculation might help.
the UA and UP are clearly related, and point to. Merope and 5C respectively; this has led to a few possible hypotheses, of which I favour the distress signal/searching for Paul variations. The UA scans our ships, but appears to do nothing, people have speculated it transmits those pictures somewhere, possibly Merope, since we see the morse (& have decoded the ship outlines it contains) & that ties in with a Galnet post about them sending information over vast distances. From a post this morning the UP response ( the chittering part of the signal) when scanned is slightly different (as yet unconfirmed, but from a creditable source) in different locations. So what if the UA is actually scanning for a Paul ship, & is transmitting the scans to the UPs. Possibly if the UA scans a Paul ship &/or the UP is scanned by a Paul ship their behaviour may be different to when we scan it.
not sure this helps, but I like to think aloud