I was checking 3 rifles this weekend for hunting season here in Colorado
Mine and my two kids rifles

I have a 100y target & 400y

My scope had parallax adjustment, I went right for the 400y target, 2” group, couple clicks adjustment, good to go

The kids rifles have cheap scopes, their rifles shot just over one inch groups at 100y, could not find the 400y target (2ftx4ft) after a dozen shots, Maybe a bullet on the corner here and there. Gave up, going to tell them 200y max

I blame the parallax.... their rifles have a super short LOP so hard to do the hold your head back trick