The Mohu Leaf antennas were designed to be placed above AND behind your television (not just behind the TV). A general rule of thumb for antenna placement is the higher you can place it, the better reception you will have.
When you place your Leaf antenna behind and above your TV on a wall or bookcase do a channel scan to see how clear your reception is and how many channels you receive. If you are not sure how to do a channel scan, contact the TV manufacturer directly as set-ups can vary. If you are getting clear reception on the channels that broadcast in your area, then you are done. If you think your reception can be improved, then try placing your Leaf or Leaf Ultimate in a window and redo the channel scan.
Once you are all set up with your antenna in the window, do another channel scan. If your reception has improved, you are almost all done. Reward yourself with some Mohu-provided couch surfing.
A final note about window placement. When you get your Leaf or Leaf Ultimate in the window and you are happy with the reception, make sure the WHITE side faces outside so the antenna absorbs less heat from the sun. In addition, secure all four corners of your antenna to the window so it does not curl (clear packing tape is fine). If the antenna curls up, it will degrade reception.
