Topband: W8JI verticals proximity to fence

[Missouri Guy]

Hi Gents,

I'm planning a 160m RX array using W8JI's 20-ft
vertical design.  What's would be considered the 
minimum distance between one element in the
array and a barbed-wire fence (that is about 1 meter
high) without disturbing the array pattern?  I'm thinking
~6m (20ft), but I have data no support that.

The end of one of the loading wires would be about
1.5m (5ft) from the fence but above it and with a short 
buried radial directly underneath.

Thanks,
Charlie, N0TT