Photoshop :: Placing Mask Behind Extraction

I used to work with another artist at a graphic design firm and he showed me a really cool way to put like an empty black, blurred mask behind people cutout or extraction which gave an illusion of depth. The mask really helped make the subject not look like an obvious knockout. He went through the steps and I should heave written it down, but failed to do so and lost the techniques.

I have been experiementing with doing a female model with flowing hair, like you see on the better fashion mags, saving the sel in channels and doing my editing there. Then I have tried using channel copies and using layer masks and it's still not the trick or result the PS artist was doing.

how I might be able to pull this masking technique out of the hat?