Compton SID
From where I live near Benson (and specifically from my back bedroom window) I am used to seeing the traffic from Heathrow on a Compton SID.
As a layman, I would have thought that this "Standard" departure means that all traffic would be approximately at the same height and position at or near CPT.
They would normally be (estimate) 8,000 - 10,000 feet, and following specific path across my eyeline, but I note quite a lot of variation, often hearing an aeroplane and not seeing it where I expect, but very much higher, or nearer to me than usual.
Is this because there is a certain amount of leeway in the procedure?