So I am at 50 skill enchanting. I enchanted my armor with fortify destruction to reduce casting cost by 8% using common soul gem(didn't have higher). Then I realized I can have insightful enchanter perk available so I assigned the point to it and enchanted the same type armor/using the same soul gem with fortify destruction to get the same result. Shouldn't it be 25% better? Anyone knows explanation?

Insightful augments enchants that boost skill like smithing, potions and speechcraft and sort I belive. Not sure why it didn't add skill to destruction directly if that's the same line of enchants.

Yeah, was this enchant the fortify destruction + mana regen enchantments seen on robes?

I would expect Insightful Enchanter to work on what you're doing.

Is it possible that you're confusing two screens? When you first look at the enchantment list it gives you a value. When you actually select the enchantment, it tends to give a different value, usually lower.

Are you sure the second values were the same? Or did the first time you just looked at the first value?

Yes I think that was the one , cannot verify for sure now. So it doesn't work since it is combination of enchant?

I am aware of the difference. Both values remained the same.

I honestly don't know. That sort of enchant has two types of effects, both that would be affected by two seperate perks. It may be that to improve that effect, you need both perks.

This is purely theorizing though, I really don't know. Usually I go up that tree just to get Dual Effect, which is worth it no matter what.