Can you describe the compass orientation of your 3' x 3' spot? Does it get full/part sun, full/part shade? What type of soil is it and how much water does it get? Burning bush is invasive here in CT so it grows in everything from full sun to full shade just about anywhere. Your ideal dwarf perennial will likely require more specific growing conditions.

If there's enough shade and moisture, you might want to check out a hydrangea. They're pretty easy to grow and require virtually zero care altho' they aren't everybody's cup of tea when they're dormant. You have a lot more options in your Z7 garden than I do--might get some ideas browsing the Santa Rosa Gardens or Bluestone Perennials' websites where you can do a more detailed search.

Best of luck!