I think you may be referring to Chroma Blur. It’s a Sony plug-in that you add before the Chroma Keyer to smooth the chroma sampling. Keith Kolbo has an excellent tutorial on this called “Gain a better understanding of Chromakey / Greenscreen / Bluescreen” on the VASST website.
The green screen tutorials you guys sent me to worked great. and each one pretty much confirmed what the other said, so I was confident they'd work. Thank you both.
Now if anyone could explain exactly what I'm doing with those threshold sliders.....