This book - Blake L, Red Alert: The Story of South East London at War, 1939-1945 - published about 25 years ago is a local historian's view of trying to make sense of the deception. I believe Mr Blake lived in Beckenham and had noticed that Bromley and Beckenham had a disproportionate incidence of V1 impacts (far more than East Dulwich). As for V1 accuracy: ram-jet guidance was pretty rudimentary in 1944. I still have a nagging suspicion from examining a plot map of actual impacts and spurious impacts reported back to the Germans that the German re-targeting of V1s moved from the West End and North West London 5-10 miles South-Eastwards towards the Pas De Calais.