The lowest reward level is set to 0.2 dollar cent, which currently corresponds to 2 Satoshis. To increase this reward, you have to wager, as you said it. But if you only have a few Sat in the account you don't get the 2 Sat but only 1 Sat.

Some month ago the base Reward should be 3-4 Sat and for a short time I got 2 Sat per roll with ~15k Sat balance.

I guess the question depends heavily on how the rounding is applied. Maybe only 30k Sat is needed to get the full base reward. The 100$ dollar boundary is for activating the 1000% Sat bonus per roll if I remember correctly.