The sense of knowing where a character is in a space in fiction is the same sense that is used to visualize anything else. It is the same phenomenon. If you can "know" where a fictional character is in a fictional space, you can also "know" how a fictional apple looks like, or how a fictional coffee smells.
How or where do you hold the knowing of the location of the fictional character? Look at that psychic phenomenon. Aphantasia seems like not knowing what psychic operations one does all the time, while someone who can visualize can consciously use these psychic operations.
Proprioception is entirely different from vision. You can know where your hand is with your eyes closed without visualizing anything. My sense of where things are in space feels very similar to proprioception, not vision.
Location and vision are separate senses. I'm completely aphantasic, but of course I can orient myself in remembered spaces. Fictional spaces are more difficult, but not impossible if the description is good.
How or where do you hold the knowing of the location of the fictional character? Look at that psychic phenomenon. Aphantasia seems like not knowing what psychic operations one does all the time, while someone who can visualize can consciously use these psychic operations.