Stonor Park

Having at last re-visited this site (see notes below) I am very confused. Its position in the park is very beautiful and tranquil, only the occasional car passing. The circle itself is mainly composed of the generic Sarsens but a curious extension to the N is made from conglomerate including the tallest stone at the termination.
There is a small double concentric prone circle somewhat N of centre of the main circle. Some of the stones are upright, some leaning and some prone. In the valley, apart from some used as road markers, there are several erect stones seemingly randomly placed.
How much of it is authentic? My own thoughts are that the circle itself “feels” right but the odd N extension looks as though an antiquarian has though to make a faux passage grave and while he was at it put a ruined cist in the circle for good measure!
The etymology for “Stonor” is, not surprisingly, “stone hill”.
This pretty circle needs more people to visit it, someone with more experience than me would be a start!