The item level of the piece you are trying to enchant also matters a lot.
You could have 100% enchanting, full percs, etc, and you will still not be able to put, for example, as much +health on a dwarven helmet as you would on a Deadric one. The deadric armor is capable of holding more spell charge.
So, it's Ench level + soul gem level + item level that give you the percents on your gear, it has nothing to do with the strength of the enchantment when DE'd.
there is no difference if i enchant fur or vulcanic glass, "destriction needs 5% less mana" stays like that
The item you destroyed only teaches you the effect, it does not lock you into a specific percent improvement. That percent will go up as your skill raises and based on the size of the soul you use to enchant.
no it doesnt. i havent put perk points into enchantment but i raised the skill for like 30 pts (20 to 50) and it didnt change anything. if i destroyed a "destriction needs 5% less mana" robe, grand soul will give me that effect and everything else is lower.
also i drank enchanting bonus potions but that didnt change anything. (same goes for smithing potions)