what set screw? that's a transfer passage for pressure from the middle of the valve to the blowback port. or maybe it has a setscrew in it you can adjust? would be nifty. but ultimately BAD, as it would encourage valve body being disassembled... which is not recommended for non-techs who want their gun to keep working just right.
what is that other valve? it's got some funky buffer going on, and nice external blowback paths. or is that the Eko valve? yea, I'm this much out of the loop in blowback tech... to think I used to call myself an expert ten years ago with blowbacks!