Yes SL - having looked at a mass of totally confusing stuff on japanese censorship I still find nothing to explain why the black bars are used and so placed.
My conculsion is that the artist has to make a concession to the censor in his works if they involve genitalia and he is not to be prosecuted. Although 99.99% of the drawing remains unadulterated and obvious, the coronal ridge (and the frenulum) is selected as a gesture, being the most sensitive part of the glans in coition.
(I think we need Sebbie on this....)
