It sounds like you are only moving the gang adjustment on the sight.... that will move ALL FOUR of your pins at once. Which as you noticed will throw your 20 and 30 pins off.
Most sights will have slots on the right hand side (if you are right handed) of the sight housing (round part). You'll notice that there are four small allen head screws that often ride in 3/16" tracks. By slightly loosening each of these in turn, you can slide your pins independant of each other up and down those tracks.
First thing I would do is space your pins out a bit... put your top pin about 5/8 to 3/4 of the way to the top and spread the rest out evenly under them. Go back out and resight your 20 pin moving the WHOLE SIGHT like you have been doing. Once your 20 pin is set... then you need ONLY move the other three pins below the top one. Remember to always follow your arrow....