There still remains a tension between masturbation as part of the phallic stage and its relation to an earlier stage that is removed from ego and object drives with external objects.
It's not so troubling to me because there isn't a problem with confluence between different stages. A person can receive transferences from more than one stage or phase at the same time.
The troubling thing at the moment is the difference between the part-ego stage and the previous auto-erotic stage.
Given that the part-ego stage involves a part-relation to people vs. their memories, then masturbation that imagines past partners or loves who were real external people seems like the candidate here.
In contrast, the auto-erotic, and its relation to internal Space and phantasy, suggests that masturbation would be based upon sexual scenes and acts which one hasn't experienced but seem exciting.
However, this once again leads us to the part-ego stage where the increased intellectual capacities lead to more fantastic creations...
In the ego (social) drives, I've discussed this as having an author who spends more time writing about his or her imaginary world then being connected to people in external Space. Such an author can have stories that are set in our world, and I see the part-ego stage as having a further rivalry with the world as such, so that, sci-fi, fantasy, and other creations are much more interesting to them.
So, it's possible that the auto-erotic stage gives us masturbation that is "perverse" in the light sense of a man, for example, who watches types of pornography that he hasn't experiences but are exciting for him (anal sex, bondage stuff, etc.). However, truly perverse stuff (bestiality, necrophilia, etc.) might require the added penchant to negate this world for another more fantastical one, in the part-ego stage.
These are just thoughts, and will require being matched up with psychic bisexuality and clinical data before they are worth much...