Possession limitations under hood - can we turn Spiritual into Parasitic or viceVersa

[Plane]

I'm trying to figure out the differences between these two and how one might grow to emulate the other by using other modifiers. Basically breaking them into components which are same or diferent.

Basically trying to figure out what makes one -60% and the other -20%

The common element of both of them is basically "your old body has to enter inside the possessed body, and it gets carried along wherever the new body goes, and the possession ends if the old body is evicted from the new body".

This also means stuff like you can get your old body hit inside the new body.

Now as for the differences:

1) Parasitic victims can resist with HT if it's higher than Will - this is defined as a -20% nuisance effect when Monster Hunters introduced it in Slayer's Strike

2) spiritual Possession can be ended by the Exorcism skill (Parasitic and other types cannot)

3) food eaten by the target will nourish the attacker in the case of Parasitism - this sounds advantageous to me so your old body doesn't starve to death while you're ignoring it - this benefit isn't mentioned for Spiritual but since the prereq is the Spirit meta-trait which includes "Doesn't Eat or Drink" it would be a moot point

We don't really have something which is "spiritual possession for insubstantial characters who don't have the entire spirit meta-trait" which seems like it would be important. In that case, something like "I can feed my original body without ending this possession" would be pretty useful.

You could even argue that Spiritual has "only while using insubstantiality -10%" built into it. Parasitic conversely doesn't require that - yeah using Permeation (Flesh) is one way, but it also works if the target has Payload or if you're a very small SM.

The only thing I can think of to account for spiritual having such a comparatively high cost might be the benefit of "my unconscious insubstantial body comes along for a free ride even though I couldn't normally take free rides".

Like if you were just a ghost who wanted to do a "body cling where I try to hide inside you and use you as cover DR" that might involve some sort of weird Grappling, but you can't maintain grapples while unconscious.

One might view Spiritual as having a very limited sort of "Compartmentalized Mind" where a semi-sentience remains behind in your unconscious body to retain a "carryalong grapple" so that you can bring your insubstantial OG body along to keep an eye on things?

Say for example we had a non-spiritual possession which had "only while insubstantial -10%" on it - you could safely be insubstantial and control some other body - but bringing that old body along for the ride if you WANTED to would require either animating that old body (I guess some kind of Telekinesis) or getting some kind of "Affects Insubstantial" on the Lifting ST of your new body? (I don't know what rules exist for substantial foes grappling-instead-of-damaging the insubstantial ones)