In one of my top five anime series of all time, Puella Magi Madoka Magica, masking is used to a slightly different end. In Madoka, magical girls fight against witches in a sort of alternative witch world- which you can see here. As this clip shows, the witch world is pretty insane- there are magical creatures, perspective and line are thoroughly experimented with, etc. Masking is used in that the iconic central characters, Miki and Madoka, remain the same, which makes it easier for the viewer to follow them into this totally nonsensical alternate reality. So, the masking is a bit different in that the backgrounds are far from realistic, but the main goal of masking is accomplished in that masking allows the 'reader' (audience) to 'safely enter a sensually stimulating world.'
I think that the most successful masking I've seen has been for this purpose- the bridge the gap between two different realities the author has created. Anyone agree?