The Arc has upward firing speakers that reflect off a ceiling - so it should ‘ideally’ be mounted no less than 4 inches below the TV - at a height of approx. 4 feet (ear level, when seated) in a room that has a ceiling height between 7.5 and 12 feet (2.3 to 3.66 meters). The adjacent walls on either side should be not-less-than 1 foot away too for the side firing (front surround) speakers.

My Arc is actually sitting on the fireplace mantle, with the TV wall mounted about about a foot above the mantle.