"We don't yet know which of these effects were intended, or whether they all were, but there are far too many for serendipity or mere coincidence."
On the contrary, I was musing to myself there are far too many for credibility!
Arguing that something exhibits "intentionality" is one thing, proposing it had LOTS of functions rather undermines the assertion, like saying a pencil was deliberately made both to write with and to hold up to track the movement of the sun. It could have been but it's not convincing. If one goes further and says it was also deliberately made to observe the corona AS WELL then it's less than unconvincing.
Nigel, this photo taken from the front of the dolmen clearly shows how 'off-centre' the capstone has become to the closure stone which is its only frontol support. You will also notice how the capstone is leaning to the left. In my opinion it is most likely that the capstone has slipped (and is continuing to slip). My main point though is that when in its correct position the 'hole' would be to the outside of the side flanker and not over the catflap area thus making your viewing position from beneath not as suitable for observation.