is that how Nxt works? this is a bit different. will show some pseudo-code asap.
the more bergstake the higher the probability of winning the lottery. the number of digits in the lottery gets smaller. the reward is always the same. and yes, micro-investors also have .01 bergstake, and can play the lotto 24/7 , probably better odds then power ball!
I don't know how NXT works. But if the investment proportionality comes in at the block reward, then the way I describe is the way to do it.
Making the chances to sign a block based on the size of the Bergstake share works just as well. The only problem is that small-time-investors will be split into two groups: lottery winners and also-rans.