MacReady's perk will affect anything called Head, and also some similar things. This includes the 'face' part of a radscorpion, and even the 'barrel' part of a machine gun turret. My informal tests indicate that none of the Mr. Handy or its variants' limbs count, although you might think the eyes would. The vast majority of enemies have a limb explicitly labeled 'head'.
This is based on my own experience having the perk on two playthroughs, including my current one. This perk used to be bugged, giving a 2000% percent boost. This was a potentially game-breaking bug that essentially set your head hit-percentage to 95%. This made it quite easy to see which body parts were affected. Based on playtime after it was patched, it's possible that turret barrels are no longer included, but it's harder to tell.