I did two runs yesterday on one we started with 100KG in the main and this burned off with the xfer pumps de-selected until 52kg only then the supply tanks started to show a reduction. We then did the second aircraft where we drained the main tank to 60kg before we started the test thinking it will take 10kg before we start to see the supply tanks dropping except we didn't. We had 12kg left in the main before the supply showed any signs of dropping.
The third aircraft the day before though started at 57kg.
I am still waiting for an technical explanation for this "phenomenon", the overflow channels are way above these levels, so the answer from RWB2 doesnt satisfy me.
HAPPY NEW YEAR
skadi