Joel Achenbach and Gene Siskel have said that many big stars happen to have physically large heads… something about they draw the eye onscreen and you have to look at them. Gene Siskel showed a shot of Clint Eastwood standing at the back of a group of people in one of the Dirty Harry movies and pointed out that his head was as big as the heads of anyone at the front of the group.
Humphrey Bogart and Tom Cruise have this physical characteristic, too - smallish-to-medium height, slender build and proportionately large head.