Both the Objective and Subjective Towers of Existence are built around a particular assumption that lies so close to their core it can be difficult to notice: they assume the existence of the self.
In particular, the notion of "subjective" requires a subject, and a subject is created by construction around the notion of its self (literally, itself). The whole idea that objective and subjective reality aredifferent (let alone that one is more fundamental than the other) requires this self-based distinction.
We arrive at a third "Tower" of Existence by discarding this notion of self, and it is what I call unified reality.
The basic idea here is that there's a single reality encompassing all of the "levels" of existence discussed above (objective, subjective, interstitial). Each of the levels is arrived at by slicing, dicing, or separating the unified whole in order to carve out just the piece in question. For example, objective reality is arrived at by carving out some pieces that are declared to be "subjects" and considering the rest, whereas subjective reality is arrived at by carving out some piece, declaring it to be the "subject", and discarding the rest.
The best way I've found to explore the unified nature of existence is to negotiate the boundaries of the self. Consider the following various such demarcations:
Your self ends at the limits of your brain.
Your self ends at the limits of your body.
Your self ends at the limits of your clothes and self-decoration.
Your self ends at the limits of your property.
Your self ends at the limits of your impact on reality.
Each of the above has some frame of reference in which it is a valid boundary. None of them is right, so much as each has some context within which it is useful. For example, civil courts often use "personal posessions" or "property" as a delimiter. For another example, at a social gathering "clothes and self-decoration" is more frequently used. For yet another example, when getting cut open by a surgeon for a transplant, the "brain" is used [1].
[1]As the newly incorporated organs join your physical body, and the surgery isn't operating on your self
It should be apparent from the variety expressed above that selves can overlap between subjects:
Siamese twins may share a physical body.
You may share your possessions.
Many people's impacts on reality constructively and destructively interfere with each other on the grand stage.
It should also be apparent that the closer two subjects are to each other, the tighter the bounds across which sharing occurs:
Personal possessions are more likely to be held in common by subjects who occupy the same domestile.
Bodily fluids are shared between sexual partners.
Thoughts [2] are shared by close lovers.
[2]I am not referring to "coincidence" in which in one intant two instances of the same thought coincide in two bodies (as with interstitial facts), but rather to where a single thought occurs in more than one body.