If you are copying the OEM tool, I don't know the dimension you are requesting. On mine, the dimension you are requesting is about 3/4"
I don't have the OEM VW tool so I can't tell you it's dimensions. If you figure out how long it needs to be, let me know.
The relief cut has to clear the valve cover and fit snugly into the slot on the camshaft. My metalnerd tool is shown below and is slightly different than the OEM VW tools pictured.
The middle "E" on my metal nerd tool sticks out by either 5/8 or 3/8. since the overall length is about 1 7/8 and one side is 1 1/4, the rest is about 3/4 or 5/8. What's important is that it reaches into the camshaft and holds the groove.