Why does my radar range change from 40nm to 160nm after I lock a target plz

[666]

I'm at a given radar range using AIM 120Cs at say 40nm and I lock a target up, then the radar range has gone out to 160nm for some reason the next time i look at it. Its not just me, my mate gets the same issue as we discussed tonight. Why does it do that plz? any help appreciated. 

Edited March 25, 2021 by 666