The value of all games you give away is calculated to two totals. One, all the games on this list and the other all non-bundle games.

The first $25 from the bundle total is swapped to the non-bundle total to give you a start.

Then the bundle total is clamped to 20% of the non-bundle total and they are added together to get your final value.

So if you only ever gave away bundle games you would get $25 + (20% of $25), which is $30.

You are giving away bundle games meaning you purchased them for a very little amount of money, (the have a * after them when you create giveaways) and they can give you a max of $25 of CV then they give you 20% bonus CV for non-bundle giveaways as long as the bonus not exceed the value of the bundle games (short: bonus = 20% non bundle game value, bonus=bundle game(s) value-25$)(also you get bonus for the $25)

Edit: it seems someone was faster than me...