No pot holes around your way then Markus
Jules the protrusion (tapered) is a form of damper, wont stop the forks bottoming but should stop the Clunk, as Markus has mentioned the thickness of oil has a lot to do with this.
However getting an oil thick enough to stop the clunk could well mean the forks are too stiff for the rest of the travel, depends on your local roads, strength of the springs and probably other factors.
The Dow type dampers provided the same effect as the bottom protrusion but for the the whole travel of the fork not just the last inch, I use 10 or 15 (sorry memory) fork oil and they seem about right for Northumberland's rural autobahns.