with the current rules you'll need to get OVER 6 btc in order to guarentee that nobody will get over 100M
I think for the category4, no matter how many btc you invest, you will not get more than 100M of coins that is also a cap for the combination of all category for one user if the user invested in multiple categories. So there might be leftover of coins for the category4 if only very few users are interested in it.