It's worth pointing out that that thesis is already well and truly falsified by the geological work. Ixer and Bevins have shown that there are various types of rhyolite represented in the debitage and in the bluestone assemblage at Stonehenge -- and they have also shown various types of foliated rhyolite from the Pont Saeson - Rhosyfelin area. In fact the famous "Jovian fabric" is pretty variable too, and I have disputed the contention that some of the fragments found at Stonehenge can be provenanced to "within a few square metres" since nothing at Stonehenge matches exactly the geochemistry and the thin section information given to us for Point 8.
Take a look at this post:
The more I look at the published thin sections and associated geochemical information, the more convinced I become that the closest match of all is between sample OU18, taken from the Stonehenge Avenue, and sample PS10 taken from an outcrop on the valley side a few hundred metres south of Rhosyfelin, where there is a sharp bend in the river gorge. These are the two samples: