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I am not clear whether I got your point or not but it seems like you didn't separate your subform. For instance, You may use as following Hierarchy:
+Level1. Main Form/ Main Page (on the content type of subform object property: you select flowed
+Level2. Subform1 (Containing your action button)
+Level2. Subform2 (Containing what you want to repeat)
Note: The add instance object is Subform2. Once you click on the action button, everything in subform2 will move down.