In meanwhile I called an expert( she is not PhD but cleverer than many ACC ATCOS). she need a little time to give an exact distance, but at first glimpse she gave me one rule:
for such triangle rule is that third side in such triangle must have distance between 33.2-18 and 33.2+18.
So minimum distance is 15.2 Nm
3 times more than minimum.
according to this example it is now clear to me why ACC ATCOs are paid higher than APP ATCOs. they need more space
