The key to not messing up your tip or blade with the belt is keep the PROFILE of the knife LEVEL when you pull it through the guide, and of course keeping contact with the guide from the beginning to the end of the contact with the belt. Many try to dive the blade down vertically when they get to the part of the blade that curves up to the tip. This is what can end up grinding the tip off your blade or scratching it.
If you follow this simple procedure you will not scratch your blade or dull the tip. I have many custom knives and I sharpen them all with the regular work sharp without any issues.