Here's an idea. Introduce a concept of causal space . In many of the approximate theories we will want to use, causal space will not correspond to real space. Causal space has points. Events occur at points.
Points persist from situation to situation.
Thus we can talk about the same point in related situations. Distance in causal space is defined by the time of propagation of effects of events. Events cannot affect fluents associated with far away points in a short time. The fewer points there are in causal space close to a given point, the more conveniently local computations can be done. We will want to work with spaces without very unlikely causal connections.