Here's what Tony at WHH had to say,

"Steve,
How big of a flag? If it's small to scale not a problem off to the side, that's where it would be put in real life. I would say you could maybe go as big as; 3" X 5".
Thanks,
Tony C."
I was looking at a 4" by 6" but may have to go smaller, what do you guys think?

sorry about the double post