One synonym for "most superimposed" could be "most overlaid", meaning that one thing has been placed on top of another. Another option might be "most stacked", which could imply a vertical alignment of one thing on top of another. "Most blended" could also be used to describe a situation where two things have been combined in a way that they are now harder to distinguish from each other. "Most merged" could refer to two things that have come together to form a single entity, whereas "most intermingled" might describe a scenario where multiple things have been mixed together in a way that they are now difficult to separate.