When you put a magnifier behind a red dot, it does indeed magnify the dot, but it also magnifies the target at the same rate. So the dot does not increase in size in relation to the target. A 1 moa dot at 1x (no magnifier) will cover about 1" at 100 yards. A 1 moa dot with a 3 x magnifier still only covers about 1" at 100 yards.
Ah ha. So what does a 4 moa dot ( no magnification) do at 50 yards?