I know, it can be tough to decide. I personally would err on the side of more satin than flat, just my choice. Given the age, or lack of, I just don't see them getting too dull under normal conditions, HOWEVER, you raise a good point about field applied finishes and less than ideal conditions and/or supplies available. The photos above BOTH seem to show a satin-ish finish; the first photo less so, but if you notice, it is taken with overcast skies (there are no clear shadows on the ground beneath the plane) and the tail panel still reflects pretty well the available light. Second picture is in full sun, with clear, dark shadows falling. Still fun to ponder!