want to try something different......go into your local newsagents and ask if you can put your leaflet in every daily paper and all the magazines, offer the newsagent a free carpet cleaning as payment,
i bet you can find 10 newsagents in a 4mile radius
if you want to use supermarkets then get a young girl to stand at the exit and just say "can i put a leaflet in your bag?" then get her to stick a leaflet into their carrier bag, they will leave it their until they get home and are unpacking the shopping
as for windscreens I think its will just get chucked on the floor