You can see that the amount of Waves tokens you receive goes down as the more BTC is invested. However, as more BTC is invested, the value of each Waves token goes up. So you are not losing out on any value, it is just being represented in an different matter (more valuable tokens rather than many tokens that each have lesser value).
Thank you for the clear explanation sir! And thanks to Bobo81 for his great work, will be useful to follow this ICO!