As it happens, I did a few hours driving yesterday for the first time since installing my Split-Charge Relay and looked at the data last time to see what was what on what is now a very similar setup to yours today ....
I started off the drive with all batteries fully charged (as said by harrow, results will vary depending on current charge levels) and I got very similar results to you - I was 'using' -10 to -15W. So around 0.7-1.2A going into the batteries (which MUST be from the Alterntor via Split Charge the way the data is logged); the MPPT controller was in float mode and providing close to zero Amps in - but it did suddenly kick in with 126W of power when the fridge started - so it seems the Solar Controller is much more responsive then the Alternator to a sudden demand (YMMV on that one on a different vehicle of course).
So I would say your system is spot on but .... I would suggest running down your battery bank to maybe 80% SOC and then running the engine and seeing what the numbers are in that case as well (ideally go for a drive with someone else driving so you can check the numbers voa bluetooth when engine running in normal circumstances).
Thanks, wildebus. That's very reassuring information.