"The church at Edlesborough in Bucks is on a high promontory."
I have seen that too its about 10 minutes drive from me. On the subject of Yew Trees and Churches there is a Yew Tree in the garden of the house next to the church in Wing, Bucks (where I got married 3 weeks ago). Wing church claims to be the oldest Saxon church in England - not sure of any megalithic activity there tho - would need to go back and have a look. However I am curious about the church in neighbouring Soulbury which is built on a rise/mound? and there is a stone (not sure if is a standing stone across the road from it - again further investigation required by young Joolio here
All the best Joolio