Good question ! I have no idea how to answer it.
To begin with, there is no clear distinction between proprioception and exteroception. Or there is one, but it relies on a specific model of what constitutes me. For exemple, an embryo is treated by its mother’s as a part of its body. When the embryo is born, it’s not directly a component of the mother’s metabolism anymore, although it remains embedded within the mother’s self-model. at some point, they’re gonna be disembedded from this model entirely. What happened ? Birth provides a clear cutting point from a metabolic perspective, but psychologically there is no clear point where the child becomes an alien, definitively and irreversibly. So is the relation between the two “interoceptive” ? I don’t know, but I do know a rigid conception of either response will lead to prediction error.
I assume the article that most directly resonate with your question would be Ciaunica, Anna, Axel Constant, Hubert Preissl, and Katerina Fotopoulou. 2021. “The First Prior: From Co-Embodiment to Co-Homeostasis in Early Life.” Consciousness and Cognition 91 (May): 103117. . I would say the notion of “co-embodiement” and “co-homeostasis” apply more widely to social group, although with widely different forms of coordination than in the case of mother-child dyadic relationships. Generally speaking, human cognition is based on a permanent dance between internalizing and externalizing systems, either as part of my (self-assessed) extended phenotype or as part of the environment being navigated. Assuming there is a “true” scale of individuation would lead to a never ending chase toward the one scale that “really” drives the other, whose dynamics would ultimately depend heavily on elements of the “environment”. The only elegant solution I can conceive of is that there is no “true” scale of agency, or rather than scale of agency (and the nature of the “interoception” it entails) is relative to specific perception-action cycles.