Sharing narrow content
Since narrow content is not determined by external factors, it depends much more on other propositional states than wide content. For example, if you believe that Aristotle was human whereas I believe he was a poached egg, the narrow content of all our beliefs about Aristotle will differ. When I believe that Aristotle was Alexander's teacher, you can't have a belief with exactly the same narrow content unless you also come to believe that Aristotle was a poached egg. Likewise for imaginings: When we both imagine Aristotle teaching Alexander, our imaginings cannot have the same narrow content.
Similarly, I think, if Ted believes that for any atoms there is a fusion, whereas Cian disbelieves this, they cannot share any imagining about atoms.