I'm not very good at physics
I didn't check it on closer distances but what you say sounds logic
conclusion : get to know the scope in changing conditions ...
I think on image the Mamba gives great value for " little" money and the floating + is a +
I'm now trying it at 7x which gives clear view up to 45 yards in both conditions , paralax at 25
this way the scope can't fool me , I'm good enough at that myself