I think it's probably just you! There's a handy facility at http://webtrak.bksv.com/lhr where you can replay the track of every aircraft arriving at, or departing from Heathrow up to the previous day. I've just taken a look at some of yesterday's flights and planes are generally at about 4500' when they come over Forest Hill. True to say that they do look closer when the sky is clear, but that's the same height they have been at for years!

Planes going into City are lower - generally more like 3000' - but they don't have Jumbos into there.