One Tolkien/Lewis distinction in Sarah Waters's talk at the conference (I think. Might've been someone else, though) is that Lewis uses a great deal more interpenetration of this world and his subcreated worlds, while Tolkien disliked it and only nibbles at the edges. In the early parts of his books that take place in Middle-Earth he suggests hobbits might still be around, the other races besides humans also, and the events of the tale just impossibly remote from our own era.* The seas and lands have all changed it is so impossibly remote (but see the footnote), yet the stars and moon are clearly ours as well as theirs. It may have simply been that from earliest days Tolkien had no interest into taking his legendarium to another planet, not even an invented one. Earth Is Room Enough, it seems.
Leaf By Niggle could be our world interpenetrating with some purgatorial land beyond, yet it is tied to no place. Wooten Major certainly has an English sound to it and clearly interpenetrates with Faerie, yet on closer look it too is a once-upon-a-time place. Tolkien wanted his subcreated worlds to be their own, and when he disliked anything about Lewis's work it was often this interpenetration, of mythologies colliding in Narnia as on the faun's bookshelf.
Lewis chose interpenetration intentionally, as it was a theological point to him that these other worlds and their spiritual lessons were reachable from here, at least for some. This may not be related to the influence of Charles Williams as we see some of this in George MacDonald and GK Chesterton as well, who are generally regarded as greater influences on him.
Williams went farther down that road to coinherence , where it is not only the story and setting that are interpenetrated, but the characters themselves. (Link from James a few years ago.) Lewis used that as well in the second and third books of the Ransom Trilogy, and I wondered if Tolkien had ever used it as well. I would say No, But Yes. I don't see it in characters being inhabited by outside spiritual powers for good or ill or merely pagan. The Nazgul and the Mouth of Sauron may be inhabited in some sense by the Dark Lord, but it is more of a subjugation than an inhabiting by him. I grant the distinction may be forced, but it seems like something separate to me. Yet the Rings of Power, and especially the One Ring have a spiritual dimension that has personality, yet the objects even more powerfully comes to inhabit their owners. They are not just +5 broadswords with a sort of ability enhancement. The objects can be inhabited, be coinhered by outside spirits, and they in turn can get into the very personalities of those who possess the objects. But not a direct occupation of a creature by a spirit.
You may find a counter-example, and I would be interested.
*I discussed a half-dozen years ago that Tolkien actually did write about time travel, if we are allowed to squint. There are medieval Catholic themes, other attitudes are more Anglo-Saxon Dark Ages, and the technology seems something like Iron Age. Yet the hobbits are clearly the late 19th C rustics from around Birmingham that Tolkien was so taken with in his youth. "[The Shire] is in fact more or less a Warwickshire village of about the period of the Diamond Jubilee." The whole story seems to depend on such people having traveled back in time and gotten stuck on the fringes of that world. Varieties of pies, tobacco, tea, recognisable musical instruments, new mills being put up. It is possible to see these as evocations rather than what were "really" in the Shire, in the same way that the language of Rohan was not "really" Anglo-Saxon but bore the same relationship to Westron that A-S does to English, so the latter was used to illustrate that effect to us.