The Audiere library stores it's volume in a "float" (32 bit floating point number) which only keeps track of about 7 significant digits. I switched my code to do calculations with "double" (64 bit floating point number) which keeps track of about 16 significant digits. But after calculation the value is rounded to a "float", so adding a very low number will have no affect. I'll have to come up with another solution.
In the mean time you can fade volume with a time expression:
clamp(((timer-start_time)/(second_for_fade*10), 0, 100)
There is no limiter that I know of. The plugin for the most part is just a wrapper for the Audiere library.