It turns out I was using the wrong power supply, that was all. Yes it certainly does do that squidgy and yummy compression; really nice.
Speaking of really nice, on a drunken whim I bought an FMR RNC on eBay last night, for some reason. Which means I now have four compressors (Behringer Composer, Focusrite Penta, Joemeek VC3Q, FMR RNC), none of which I particularly need, but seem to enjoy owning.
I should probably sell one or two of them.
Or! Find a use for them. I've been buying microphones as well.