Audio Compressor Inconsistent Limiter Threshhold Performance

Hello Forum,

I am having a struggle with an issue I've been aware of for a while with the Logic Effect "Compressor" in FCP10.1.4 (issue goes back at least several versions). The "Limiter Threshhold" section of that effect performs inconsistently - when it is set to "0dB" it sometimes, but not often, seems to actually engage at 0dB. Most of the time, it seems to engage at -6dB. This is confusing, but not much of a problem as long as it is consistent - however, it is not. So, calling all you audio experts on the forum: can anyone explain to me what I might be missing, what determines when it bangs at -6 and when it bangs at 0? Any advice is greatly appreciated - I use this effect on nearly everything so it's kind of a habit, but what other options do others use to compress/limit their audio?

Thanks!

Eric D - CoralVision