Venus effect explained in greater detail?
The Venus Effect is just as you understand it.  The painting the effect is referring to is depicting the woman admiring herself in the mirror, when in fact, if you study it properly you will see that she would not be able to see herself in the mirror, but she wuld be able to see the artist (or you) as the viewer.

If you look at the diagrams I put together below, you will see from the first diagram how the venus effect works.

Image 1:  The Venus Effect in play.  The viewer can see Venus, but there is no way Venus can see herself, when in fact she can see the viewer in the mirror.

Image 2:  The Venus Effect is not in play.  The viewer cannot see Venus, Venus can see herself, and she cannot see the viewer