I cannot understand bonus on the last round of an IEO. Even if they give 1000% bonus to investors, it doesn't differ.
The purpose of those bonus is to make sales even at the last minute of that round. They are pursuing more people to buy their token at their sale because they want to sell out, as in total 100% sales for their token.
It's their strategy so that's why they create promotion like giving bonuses to the last round to encourage and attract more investors. Probably a desperate move if the bonus is near to the end of their IEO.
They are only thinking of the funds that they are going to raise and not the consequences of giving to much bonus, it just encourages dumping, no wonder we are seeing peice lower than 50 to 90% because of the very huge bonus they are giving to late and early investors, in the end they are just harming their project.