If it finds the restriction there, it does not check HKCU for the restriction. Typically, you use HKCU for restrictions. The keys and values may already exist in HKCU for this purpose too. However, if you want to use HKLM, you can. You may need to create the appropriate keys and values to make this work.
All values are in hexadecimal.
This logic uses a bitwise left shift to decide which drive to use. Binary 0100 has the hexadecimal equivalent of 0x4. This is how you calculate the drive to disable. Left shift binary 0001 by 13. To disable multiple drives, take each of the individual hexadecimal drive values and add them together for a composite hexadecimal value for the registry.