Mana Cost Calculation

Hi, I was doing some calculations to confirm my mana cost and found something strange.
I'm using a 6-link Firestorm on a Pledge of Hands and a Voidbringer, my firestorm lvl 19 is linked to Added Cold-Added Lightning-Concentrated Effect-Increased Crit Damage-Item quantity, my CE has 20% quality and I have 12% mana cost reduction from the tree.

Technically my mana cost should be:

25(base cost) x 1.3(Added Cold) x 1.3(Added Lightning) x 1.6(CE) x 1.3(Crit Damage) x 1.3(Pledge Spell Echo) x 1.8(Voidbringers) x 0.85 (CE quality) x 0.88 (mana reduction from tree) = 154

But in the game it says my total mana cost is 172 and doing some calculation I found out why.

The reduced mana cost of skills on the tree only uses the BASE mana cost of the skill, so if you have 10% mana reduced, a skill that costs 10 and link it so it goes up to 20, the reduced mana cost will only use the original value of 10, giving you 1 point of mana of reduction and a total of 19 mana cost.

Its that supposed to work that way???

I heard that moving your links around can cause a change in mana cost because it is being calculated and rounded after every support.

But anyway the CE quality and your passives are additive with each oter not multiplicative so that might be it also.

In that case the total mana cost would be even lower (151 to be exact). Since we usually get the worst possible mathematical outcomes on calculations I decided to pick them separately.

I also used my Arc gem to confirm this, since it has a mana cost of 25 and its links dont have mana multiplier.

25 x 1.8(voidbringers) x 0.88(reduced mana) = 40

But the game shows mana cost 42

25 x 1.8(voidbringers) x (25 x 0.12)(Calculating reduced mana using only base mana cost) = 42

And to apply this on OP:

"

Adser wrote:

Technically my mana cost should be:

25(base cost) x 1.3(Added Cold) x 1.3(Added Lightning) x 1.6(CE) x 1.3(Crit Damage) x 1.3(Pledge Spell Echo) x 1.8(Voidbringers) x 0.85 (CE quality) x 0.88 (mana reduction from tree) = 154

But in the game it says my total mana cost is 172 and doing some calculation I found out why.

25(base cost) x 1.3(Added Cold) x 1.3(Added Lightning) x 1.6(CE) x 1.3(Crit Damage) x 1.3(Pledge Spell Echo) x (1+ .8(Voidbringers) - .15 (CE quality) -.12 (mana reduction from tree))
= 114.244 * 1,53 = 174.79

aaa ok, thnks for explaining that