DON'T GET YOU BRITCHES IN A BUNCH, ABOUT USING AN "F" FSB WITH AN A1 OR A2 UPPER RECEIVER !!
IT'S NOT WORTH THE HEADACHE. AND TOO MANY PEOPLE MAKE A BIG DEAL ABOUT IT FOR NO REASON !!
If the 1mm Front Sight Post Height is a problem, I would suggest taking the Sight Post out, and taking a Jewelers File and gently removing that 1mm. Then add a little Cold Blue, or Sight Black, and call it done.
I know that this is a couple of days old already, But, with the "F" FSB being 0.040" Taller then the Standard FSB, People have to keep it in their minds that 0.040" is only 1mm.
When yon turn your Front Sight Down 1 Click, if that equals 1/4" (or .250"), that's greater then 5mm's difference (if I'm correct).
I run an FN A2 Upper with a 16" Palmetto CHF Barrel that has an "F" FSB, that is Extremely Accurate so far out to 300 meters with Open Sights. I have not been able to go out any further, due to range restrictions.
I will be going out into the desert to do some distance shooting when it gets a little cooler, for longer ranges. I'm hoping that I'll be able to keep my shots on target out to 600 meters.