I would create a different object factory for each object (and put the collision object inside the prototype object that each factory creates). Or have i misunderstood the question?
You’d have to access the z-layer to work out if click 1 is on object 1 or object 3. And be careful… that way of doing things is going to make clicking on the small house in tile 3 very difficult!
I don’t think it will have much of an impact performance wise. You can increase the default cap of 128 factories in game.project in the Factory section.