The dot covers the target and a 4 moa dot turns to a 12 minute dot with a 3 power magnifier.
No. If it is a 4 MOA dot unmagnified then it will be a 4 MOA dot magnified as well.
As far as red dots and magnifiers go, there are an awful lot of people offering opinions who don't even understand what they are for.
1x Red dots are for speed. They are primarily used to shoot people. They make shots inside of 200+/- yards or so extremely easy with both eyes open and no need to line up iron sights. They are not dependent on light conditions or eyesight. There is no eye relief or cheek weld issues with them. Put the dot on the target and press the trigger.
They make shooting and hitting fleeting, fast moving targets under stress much easier then with iron sights or magnified optics in the close to medium ranges. Where they fail is in target identification. In the 100+ yard realm it can be difficult to see whether someone is hiding an AK under their shirt without magnification. Also small or partially obscured targets can be difficult without magnification. This where the 1x-?x scopes come in. They offer the magnification to target ID better and some have reticles and/or turrets to better facilitate shooting at longer ranges, however like all scopes they suffer from having to attain the proper head position and eye relief. None are true 1x no matter what the companies tell you. Combine that with the fact that you are looking through a long skinny tube and it means that up close (i.e. measured in feet) they will always be slower then red dots. Most do not have truly daylight usable dots. They are much harder to shoot from awkward or unconventional positions.
Enter 3x and 4x magnifiers. They allow one to run a red dot with all of it's advantages up close and with the flip of the wrist be able to target ID, hit smaller obscured targets, or make hitting targets out to 300-400 yards much easier. For most soldiers, police and civilian protection uses they work wonderfully. They are not scopes and are not supposed to take the place of conventional scopes.