I cant see from the screenshots but I imagine your Dynamic Material instance is only one variable in one actor like your level blueprint or something. You need one Dynamic Material Instance for each well, instance, that you want to make a variation on the parameters thereof during runtime.
So the most intuitive thing to do is make that dynamc material instance be a variable on the blueprint class of the actor that has the mesh youre applying it to. that way each actor has their own dynamic material instance variable and its parameters can be altered independently of the others instead of all of them drawing from the same dynamic material instance and therefore all of them changing in the same way.