I know it is 4" coz I measured it!!! and THAT is why his windows open
over my garden! [well not any more since i extended the fence tops]

You realise that this is the ideal spot for extra smelly compost
(including human waste - I believe urine over the top of the compost was
an old gardeners favourite to encourage decomposition) - or if you can
think of any flowers that are particularly pungent, or attract insects
like there`s no tomorrow :-)