Green Satin or DD 62 M had fairly narrow downward pointing beams and were not believed to pose a significant detection opportunity. We were told.
GS depended on reflections that were transmitted fore & aft!
It would have worked at its best if the transmissions were dead ahead and the a/c was flying towards a cliff face.
If it had transmitted straight down, it wouldn't have worked.
So there was a compromise was reached at about 30 degrees.
The worst conditions were when the a/c was flying over smooth water, such as the Med an a quiet day. The signal hit the water and bounced off away from the a/c.
This was a problem for 13 Sqdn PR9's at Akrotiri.