For games that support raw mouse input, the WPS field is disabled. If L4D2 supports raw mouse input, I must have missed it, and should update it.
If they are marked as "affected by WPS" that means that they do not have the option to use raw mouse input. But games do get updates all the time, so this may change over time.
Anyway, the default value is 6 (this is 1:1, effectively the same as raw mouse input)