I was enchanting a hood and with a greater soul I could get 18 points Mana boost, but with grand it shot up to 28.

Why is there such a huge difference between greater and grand?

Do we know what % of base enchant each level of soul gets?

Also where on earth do I find non-enchanted robes

Also why does enchanting svck?

If you have +100% stronger enchantments and the +25% magic enchantments you still only have 125%

So the base 20 percent for the magicka regen enchant times 2.25(or + 125%) is only 45, which is 5 less than the STARTING robes.