I'm sticking to my guns on this one.

Yes, the thicknesses can vary - but not as substantially much as this!
I have seen and handled Caithness vases in this shape, the bases are
supposed to be about 1.5 inches thick.
But it's the fact that I've seen
so many of these lightweight ones around in charity shops, (they don't always have the irridesence) I've handled them - they just do not have a Caithness "feel" to them. The walls of the glass where it is thin is
too thin for Caithness.