If you raise the input signal gain to the compressor, the compressor will be forced to work sooner as that raises the threshold of the trigger point.
You're not necessarily going to hear an obvious effect other then the volume of the program remaining more constant, which is what a good compressor should be doing anyway.
.. I sing through the channel the la4 picks up my voice.
I cannot tell the difference between whats going on unless I apply harsh compression or limiting. ..
..presumably that means listening for the effect during playback (rather than while you're tracking
Perhaps patch it in so you can experiment with it on uncompressed sources, that gives a lot more room to 'play and compare 'a/b style etc.
You could also set up a track with some distinct challenges' to throw at it. Like a good perky' vocal that also has some real hot spots in it. Set it for general leveling, then how does it handle the 'big hits..
Very often there is a lot of a comps action triggered in (from ) those first few ms of transient.