It is hotter over top of the fire than at same distance on the sides due to

Heat due to radiation process spreads uniformly in all directions. 

Air is fairly a bad insulator. So heat transfer due to conduction process is fairly less. 

But convection of heat by air makes the big difference that we observe. Hot air near the fire is lighter. It is pushed up due to buoyancy, being replaced by cold air. So there is more heat transferred towards upward direction than to other regions around the fire.