Great question. This is something I had thought about in the past, but never followed through with searching for the answer.

Many things affect  plugs, Hot plugs are made  with a large bore, a thin wire element, and the content of which metals are in the wire, rhodium , is  one  that  makes for a hot plug
and depth, if you put a short or medium plug into engines that call for longs, the plug will  be  cooler than if it was set  to depth

Randy