yes thats easy, more risk for more bonus.

In this particular case, big bonus can be allowed, considering the long roadmap, this is actually risky, so some reward is good to attract investors for the first serve tokens, so the ones that wat more, could enter the pre-sale.
Giving big bonuses will not attract serious investors that will hold your token for a long time, most of them will just ICO flippers and you will be left with a handful believers.