Most calculations work this way:

(a - b)(c - d)
a = base value
b = numerical changes
c = 100%
d = percent changes.

The champion points will follow suit. If it adds a numerical value its part of b and if it adds a percent value its part of d.

Example 1.
Lets assume the following
Base magicka cost of an ability cost = 1,000 magicka.
A numerical decrease in cost of 200 magicka (from jewelry enchant)
Set Bonus with 8% reduced magicka cost.
Passives for 21% reduced magicka cost.

Then:
New cost = (1,000 - 200)(1 - 0.29)
New cost = 800(0.71)
New cost = 568 magicka.

Please note the above was just used as an example. Currently on PTS the values are either bugged or not correct. IE: 21% reduced magicka cost is actually only ~18.5%, and the jewelry enchants that reduce cost by 200 is actually giving 213 reduction. Not sure whats up with that.

Examples 2:
Lets do a different type of calculation this time.
Lets assume the following.
Base Block Cost of 1300 Stamina. (assume its this)
A numerical decrease of block of 400 stamina (from jewelry enchants)
Passives that reduce block cost by 30%.

Then:
New block cost = (1300 - 400)(1 - 0.3)
New block cost = 900(0.7)
New block cost = 630 stamina
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The values for the champion points up to 100 look like this:

https://docs.google.com/spreadsheets/d/1toa6WFzSwn21JZ6IL6jOZKSj6pXZCVzBy_xHBP0KGDs/edit#gid=900954785

There is a table near the bottom. If you want to know what passive gives what just plug in however many points you want. This spreadsheet is a very small part of something I am working on.

Anyone? Is there any kind of logic behind these calculations? (not behind the Passives, the stat increase i mean)
It´s important!