Wow! I got behind on this. But, here's what I've found:
The Blake's hitch didn't perform so well in ArborPlex or my Velocity rope.
I have since switched to a Helical hitch and all slipping and sticking problems have gone away.
The Helical holds securely and slides freely when unloaded in both ArborPlex and Velocity. I use if for DRT tail and as the friction knot for my foot loops.
I was immensely impressed by the increase in performance of the Helical hitch over the Blake's hitch. The Helical breaks completely free when unloaded and pushed upwards from the bottom of the hitch. It's also easier to descend on - it's smoother and takes less effort to get it to break and start descending.
The Helical is my goto hitch now. I doubt there will be any turning back.
I guess this is in order too. I developed my own version of the bowline terminating knot for the Helical hitch that allows it to be tied with only one end of the rope and it can be finished off in a Mountaineer's stopper which orients the tail of the bowline straight down.
Helical hitcha bit more close up