As stated previously, the angling of the bottom cymbal has two purposes: prevents airlock and improves "chick" & slightly-open sizzle sounds.
Most users tilt the bottom cymbal- and therefore, also the top one, when they're closed- downward toward the player. I've found that this creates a tiny bit of offset... not "gap", but, laterally, the cymbals no longer sit edge-to-edge, and the upturned edge of the bottom cymbal is now exposed, which really chops into my sticks when playing with the shoulder. I resolve this by turning the upper pipe of the HH stand 180° so that the cup tilter is on my side of the stand, which tilts the cymbal(s) slightly away from me. The downward slope of the top cymbal's bow ensures that its playing surface is not completely tilted further than parallel to the floor, but now that exposed edge of the bottom cymbal is on the other side, away from me and the shoulders of my sticks. Sawdust issue resolved.