Tracking The Hive Mind - when will the hive ship appear

[ToHisWorld]

In Imperial Campaign, I have an objective "kill the hive ship" in order to pinpoint the Tyranid mothership/acient one location.

I already know the hive ship is that kind of large ships in the previous mission battle. However, I don't know how large the Tyranid invasion will come with hive ships.

The single invasion fleet point now is 750, I've fought a 2250 point invasion and the largest Tyranid ship was just battlecruisers, not hive ships. Is 750 point still not enough or just because of bad luck?

[ToHisWorld]

Reply my own question:

After two or three invasions, I leveled up and the fleet point raised to 800. Since then, every 1600+ Tyranid invasion come with at least one hive ship.