For me, tip up vs. down varies by knife. Some knives, I draw by grabbing just the exposed part above the pocket. For those, tip down actually works better for me (easier to maneuver the handle into the palm of my hand, at which point, my thumb or index finger are positioned well for the thumb stud or flipper). On others, I draw it by grabbing the handle deeper in the pocket (usually with my index finger at the bottom of the clip and thumb on the opposite side of the handle). For those, tip up works better for me, as the handle will already be positioned right in my palm, and my thumb will be positioned right by the thumb stud or hole.
I also prefer deeper pocket carrying, which will sometimes make tip up not a viable option. For example, with the Leek, a tip up carry leaves over an inch of the knife above the pocket, which is too much for me. As a result, I carry that one tip down (and with the safety engaged). Tip up does usually seem to leave more knife exposed due to the clip's mounting position. I don't mind it in some cases, as long as the difference isn't too great.