Unit size

[Septimus Severius]

This is the from the original post:

Quintus Sertorius' Guide to Conduct Becoming of a True Roman (Redux for EB)
Armies
Polybian
The Roman core of a Polybian consular army is two legions, represented by the following units:
1 unit of Velites
1 unit of Accensi
2 units of Hastati
2 units of Principes1 unit of Triarii (or two if you're playing with half-sized maniples)
What does he means "if you are playing with half -sized maniples"?
I thought he mentioned the unitsize patch , am I wrong?