I have 13" flange hat top; paired with a 13" mastersound bottom. The two cymbals are pitched at a perfect intervals (trials and months long search). The flat edge meets the hammered scalloped edge perfectly for the right amount chick and air release.
When two flange hats clasp together...
It depends on the cymbal. Play it both ways and see which way SOUNDS better. Personally....
1) 20" Swish edge up (bell right side up)
2) 18" China Boy High edge down (bell inverted)
3) 18" Z Custom China edge down (bell inverted)
4) 14" Swish edge down (bell inverted)