I have discovered a more accurate way of testing for the black curtain issue. I don't see it in 5% ire slide, but I have seen it pop up in content, mostly ones with fluctuating black levels. When the black level creeps up in the content, the flames will show in the area between 0 and 5% ire.
Easiest way to check this is to look at a 0% ire slide, which is all black. Turn your brightness so that its completely black. Then turn it one click up. The screen should be completely gray, but a very very light gray.
When I do this I can clearly see the vingetting, about 2 inches on each side and this is what happens with some content that don't have a consistently correct black level.