I spotted an anomaly in the IS freighter growth.

Normally, freighter growth rounds down. However, if the amount of colonists generated is below 1 kT, it will round up. So a fleet containing only 1 kT of colonists will grow another 1 kT of colonists per turn i.e. 100% growth rate!

The expense of deliberately building ships to exploit this is prohibitive, not to mention that the fleet limit provides a hard cap on how much pop you can pull out of thin air this way. But, well... here's yet another case where IS's micro ceiling is way off in outer space.