So basically what happens when using the summon command.

So when using this command:

summon ArmorStand -1146 30 658 {ShowArms:1,Equipment:[{id:diamond_sword},{id:iron_boots},{id:golden_leggings},{id:leather_chestplate,tag:{display:{color:16711680}}},{id:skull,Damage:3,tag:{SkullOwner:Dinnerbone}}],Small:1,Invisible:0,DisabledSlots:31,NoBasePlate:1,NoGravity:0,Pose:{Head:[0f,0f,-90f],Body:[0f,0f,0f],LeftArm:[0f,0f,0f],RightArm:[0f,0f,0f],LeftLeg:[0f,0f,0f],RightLeg:[0f,0f,0f]},Rotation:[225f,0f],CustomName:Dinnerbone,CustomNameVisible:1}

You get the smaller version of the armor stand, and as you can clearlly see in the picture bellow, the head has the same achor point as the biger version (when not using the tag Small:1), also the head makes itself big as the normal armor stand.

So the small version of the armor stand has the achorpoint (for head, the rest works as intended) of the normal one, wich as show in the picture the head turns 90 degrees sideways as opesed to the normal one.

So basically all you have to do is make anoher achorpoint for the smaller version of the armor stand (for head). Also fix the head resize thing. This also may fix heads apearing above when summoning baby zombies with custom heads.

See the anchorpoint in the second picture.
Good Luck!