For 1/4 at 100 yard scopes:
25 yards 16 clicks = 1" (or x4)
50 yards 8 clicks = 1" (or x2)
100 yards 4 clicks = 1"
200 yards 2 clicks = 1" (or x.5)

Like Solitary Man mentioned you need approx. 24 clicks to move the poi 3" at 50 yards. As too why you never saw any gain human error is typically the cause for such an event - either mis count, inverted turns, shooting, etc. It is possible that your scope is experience problems though, I would try moving it the remaining amount and shoot a group to see if their is any gain. If moving it another 8-10 clicks doesn't show any POI movements return it to the store or zeiss.

Good Luck