I did the first test in my kitchen with the overhead lights. I was staring pretty hard at the black dot looking for truly opaque. Since I have everything here anyway, I followed the test as you suggested, but outside and not in direct sunlight. 70 is all but invisible at a glance under those conditions, so 80 would be the reading.Your CYA is pretty high to attempt to SLAM. You said you could not see the dot at 70 but could at 90? That is odd.