minecraft-java-edition
The type of armor (in this case, I don't mean the material, but whether it is a helmet, chestplate, leggings, or boots) helps determine the number of armor points that the equipped armor adds. Is the armor type also taken into account in determining how effective an enchantment is?
For example, say you have Blast Protection IV on a pair of boots; will that enchantment negate more damage from explosions if instead placed on a chestplate?
First note that the Enchanting page on the wiki says that Protection, Fire Protection, Blast Protection, and Projectile Protection are all mutually exclusive, but it looks like you can have Feather Falling on boots with one of the other enchantments.
The Armor page linked in the question has a table of "Enchantment Protection Factors" provided by each enchantment. I have duplicated the relevant parts of the table below:
Since increasing the level of the enchantment only increases the EPF, when trying to find the "best" protection it is only worth looking at the highest level enchantment. The article also says that in order to maximize protection from a particular kind of damage, you would need 25 points of protection for that damage type.
Since there are 3 different types of damage, one would need 75 effective points of protection, but since each armor can add either up to 11 points to one type of protection or 5 points to each type (which is like adding 15 total), the max is 60 effective points of protection. So, you can't max out everything. And plain Protection can't be maxed out at all. Therefore, the best armor depends on what you are looking for:
Put Protection IV on each piece of armor. This will give you 20 points in every type of protection. As a side bonus, if you put any level of Feather Falling on the boots, you will max out fall damage protection.
Again, put Protection IV on each piece of armor. Adding Protection IV to a piece of armor adds 5 to each protection type, so it adds 5 to the average. Adding any other protection enchantment adds at most 11/3<5 EPF on average.
Put Protection IV on all 4 pieces of armor.
Put Projectile Protection IV on two pieces of armor, Blast Protection IV on one piece of armor, and Protection IV on the last piece of armor.
Put Projectile Protection IV on two pieces of armor, Fire Protection IV on one piece of armor, and Protection IV on the last piece of armor.
Put Blast Protection IV on two pieces of armor, Projectile Protection IV on one piece of armor, and Protection IV on the last piece of armor.
Put Blast Protection IV on two pieces of armor, Fire Protection IV on one piece of armor, and Protection IV on the last piece of armor.
Put Fire Protection IV on 2 pieces of armor and Protection IV on two pieces of armor.
Put Fire Protection IV on 3 pieces of armor and Projectile Protection IV on one piece of armor.
Put Fire Protection IV on 3 pieces of armor and Blast Protection IV on one piece of armor.
According to the Minecraft wiki:
Horse armor cannot be enchanted in survival mode, but you can use an anvil in creative mode. Enchanted horse armor will not have any effects on the horse.
So no, enchantments to horse armor will not have any affect on a horse. In addition, the armor will not "glow" as if it was enchanted.
Best Answer
No. Every enchantment has the same effect regardless of the armor piece. Protection enchantments are added together and taken as an aggregate, not per armor piece. Protection IV gives the same level of protection on boots as it does on a chestpiece. Therefore, it doesn't matter.