As a general rule, as you get closer to all the way in (stiff) on the adjustment, each click should make a bigger difference.
What is your oil level now? How much preload on the springs? What about static sag (how much do the forks compress under the bike's weight)? Do you have the right springs for your weight?
In my experience, raising the oil level makes a dramatic difference in bottoming resistance but does not have a big impact on the first 1/2 of travel.