It looks a lot like a Fishermans knot, so wonder if it has different thickness issues as well.
Does no one use a highwaymans hitch? Or has the Ray falconers knot replaced it for some reason?
Might be worth checking out the other prussik style knots people have mentioned. Think it might be catching up with the bowline for knot with the most varations.
My understanding is that it can be used for different thicknesses. I have tried it successfully with different thicknesses, but not under overly heavy loads.
Pardon my ignorance, but what's a Ray falconers knot? (never mind, I googled. Same as Siberian hitch) I just like the ease and quickness of the Siberian hitch for the first end and the trucker's hitch on the second can get the ridge line super taut.
I use a couple of variations of the prussik and find them to be extremely useful for many things.