Circles show new fresh JK growth...the visible growth only.
The line is my suggestion of an absolute minimum distance a new barrier would need to be, in order to prevent JK disturbance and reduce its growth rate. This would become as meaningless as the present one in 2 years if eradication of JK were not engaged with at these sub-sites.
To actually check its growth, then begin its eradication, would require test pits, soil-sifting and analysis outwards(left above) at least to my projected line, once the necessary barriers were in place.
A spraying and soil-sifting regime, monitored and implemented as a longterm and ongoing action, can be part of a remedial plan running alongside the site's development.