The minimum POA -> POA20 transfer reflects the transaction cost. We chose this as it costs 3 POA for the transfer. Since POA Network is sponsoring the cost during the trial period, we wanted the cost to be 1% of the minimum transaction:
3 POA * 100 = 300 POA for the minimum transaction.
The minimum transfer will change when after the trial period when POA will not be sponsoring the transfer fee.