The percentage of a potion that is rised up with enchantments doesn't count, but the base fortify marksman potion does. So if you have a high alchemy skill, the potion will raise up your skill fast.
Anything fortified with an enchantment is subtracted towards skill, that iincludes enchantments towards potions.
Goddam milk drinkers. They come in here with their half donkey untested beliefs and they are absolutely sure that they are right. They are so sure that they don't even bother to test it. No. They just say whatever they believe and that's it. Big Iron on His Hip, you are one such milk drinker.
Here is the test I just did.
I loaded up one of my characters,
Test 1: I shot an arrow with a bound bow and killed a deer 18 experience gain.
Test 2: I shot an arrow with a bound bow after drinking a 85% fortify marksman potion. 18 experience gain.
Test 3: Added Mystic Binding perk in Conjuration. Shot an arrow with Bound Bow to kill a deer. 24 experience gain.
You get x amount of experience point each time you shoot an effective shot into a target. That x is base damage of the bow. You get 6 experience points for shooting and killing a skeever with a Longbow. You get 19 experience points for shooting and killing a skeever with a Daedric Bow. You get 6 experience points for shooting and slightly damaging a mammoth, you get 19 experience points for shooting and damaging a mammoth with an iron arrow.
You get the same 19 experience points for using a tricked out Legendary Daedric Bow enchanted with awesome Fire and Lightening Damage, wearing all your fortify archery gear for 200% damage improvement. Drinking your 100% fortify marksman potion, and killing an Ancient Dragon with one awesome sneak shot, doing 3000 damage. Yes. Your experience gain from that awesome shot is the same 19 points that you get for killing a skeever with your vanilla daedric bow.
Smithing improves damage, but does not change the experience gain.
Enchanting with fortify archery improves damage, but does not change the experience gain.
Poisoning your bow with damage health potion improves damage, but does not change the experience gain.
Drinking fortify marksman potion improves damage, but does not change the experience gain.
Longbow: 6
Elven bow: 12
Bound Bow: 18
Daedric bow: 19
Bound Bow with Mystic Binding: 24