While most dot sights are advertised as having 3 or 4 minute dots, only your eyes can tell you what size they really are. The remaining experiments were conducted with only two different models of sights. The 30mm sized models of the UltraDot and the Tasco ProPoint 2. They were selected because they are both in the same price range, enormously popular among bullseye shooters, and certainly very different indeed. The most popular misconception about dot sights is that some are blessed with complete freedom from parallax.
Parallax exists in all dot sights because of the nature of the sight design itself.
While it is true that all sights do adjust for parallax at particular distances, they become more vulnerable to the problem at other distances. This is a factor with a dot sight because its reflecting lens is optimized for reflecting the image of the LED right down the center of the tube into your eye. If the pistol is held incorrectly and the shooter views the dot near the edge of the tube, it will not actually be pointed at the actual correct point of aim. In an attempt to correct for this, the reflecting lens is concave. Unfortunately this design is only somewhat effective.