as in lets say for instance you mount it above an actual fire place, which will be about 4 foot something, for comfy sustainable telly viewing that wont kill your neck you need your seat to be positioned x feet back from the telly.
on the same principle of not sitting in the front row of the cinema if ya know what i mean....just be cautious of this when its about a fireplace. In my house i have somewhere where there should be a fireplce but thereisnt so i can put it at whatever level...