I'm doing some experimentation on that but in general it's a question of how small is small. The larger an account is the faster it grows, which means that the hardest moments are the first ones. It feels like around 100 SP is a key watershed moment.
You definitely don't need to buy in as big as I did to get recursive growth going.
in initial stage a steemer use to starting investment of 50 steem through which they judge the income after that may be they invest more @tcpolymath