Well all the questions are asked I think. I too don't consider the consumption
to be "significant" although I'd keep watching.
Bedding of the rings (properly or not) would be my wildest guess followed by Oil
ring alignment at assembly. There are obviously end gaps on the rings and they should be staggered from each other during assy.
Very very rarely the assembler may not get this quite right. It usually shows up as big blowby and bad compression
from day one.
It sounds like you are running the engine
hard which is a good thing and with no other mysteries to report I'd drive on till something changes.
The only other thought is that it might consume a larger amount during warm up and basically nothing once thermally stablized. That could explain the variation in consumption
for 10 hours vs. 60 hours. The lack of smoke is perplexing but again we are talking about pretty low consumption.