We could really use a concrete example. Let's say this one is on KICKICO:
https://www.kickstarter.com/projects/ramybadie/unstable-unicornsthe creator indicates what the backer will receive for pledging a certain amount of ETH. By making a pledge, a backer receives this award, as well as the equivalent amount of KickCoinsI pledge $20. Creator indicates I get the Black Box Edition. The campaign is successful, I receive the Black Box Edition (cost to backer $15 maybe?) and the equivalent amount of KickCoins ($15).
Which is very different from: I pledge $20, the platform gets 4% of $20 and 4% Unstable Unicorns tokens. And I receive 4-8% of $20 worth of KickCoins and 96% of $20 worth of Unstable Unicorns tokens. Which by the way also doesn't add up. Where does that other 0-4% worth of KickCoins come from? That's funded by the growth of other campaign tokens?
For ICO campaigns, the platform fee will be 4% of collected ETH, and 4% of the campaign's tokens. In return, we provide from 4 to 8% of the KickCoins (in effect, selling our KickCoins to the campaign creator in exchange for the fee). Those KickCoins will be given to backers, together with the campaign tokens.
For crowdfunding campaigns, we give backers from 4% to 20% of the value of their investment as KickCoins, depending on their reputation on the site (Karma scores). This rate is being taken from exchanges, but will never be less than 0.0005 ETH per KickCoin (1 ETH = 2000 KC).This system ensures that in both ICOs and crowdfunding campaigns, the backer gets cryptocurrency for their contribution.
Let's take an example to explain better: a campaign sets a cap to raise 100 ETH. After 100 ETH successfully raised - 96 ETH will go to the creator, 4 ETH will go to the platform as fee.
KC will be generated at a price of 1 ETH = 2000 KC (or at the rate of exchange if the price for KC is higher on exchanges). Thus, there will be 8000 KC generated to give backers. So if a backer pledged 1 ETH to the campaign he receives 80 KC as a bonus (2000*4%).
Thanks for the explanation, looks like I failed to make the distinction between an ICO and crowdfunding.
So the 4% minimum bonus to backers is guaranteed because that is the fee taken from the creator, and the rest of the bonus depends on the success of the platform.
Would it be possible to trade your coins at waves platform? 
