Mike.....Silbury as 'a sort of Tumulus on steroids' that's a great comment, and you sure are right there. Indeed Silbury has a very strong energy field around it which i pickup even from near the car park area, and when you used to 'officially' be able to climb the summit, i used to go virtually boss-eyed from it's energy emission.
Thanks for putting it forward, that Tumuli/Barrows potentially act as kind of Orgon Energy Accumulators. That so far seems the most plausible explanation so far for their purpose, and as you say, their potency would be greatly enhanced when placed on an energy line, or intersecting energy lines in the landscape.
Have you had the chance to dowse for evidence of energy coming in or coming out the top of Tumuli/Barrows? Though i have tried this a little at Seven barrows, in an ideal world with the right resources i would want to dowse higher and higher above the mound to get an inkling how far up into the sky the energy may go. Of course it is possible that the energy would continue on up out of the earths atmosphere into the universe.
It's very interesting that you talk about sites such as Stonehenge/Avebury, 'showing radial and spiral forces leaving their centre pulsing out in every direction'. The reference to radials particularly pricks my ears up as this correlates with the same findings myself and dowsing partner obtained at Stonehenge/Avebury. We deliberately avoided until now any books/websites/forums which discussed dowsing findings at these sites, so that we would not be mentally influenced by other peoples results.
We have spent the most time at Avebury dowsing the energy system there for the last two years, and the radials certainly feature as a component of an increasingly unfoldingly complex multi-layered energy system. Aside for the need to get in other dowsers on site at Avebury (i must thank Adrian Incledon-Webber here as he kindly met me at Avebury to test some of the preliminary results) with us to perhaps add validity too,and hopefully corroborate our findings, it's encouraging to get same/similar results at energy sites from people of experience as yourself here on the forum.
Thank you for your informative replies Mike.