Rate of units in the army

There is a criterion in the composition of the army. Infantry or archers must be min. 30 %.
In the case of 7 units it means min. 2,1 (if should rounded up 3) units must be infantry or archers.
When I try start a battle with 7 units it is not allowed to start with 4 heavy + 3 infantry or archers only if i change to 3 heavy + 4 infantry or archers.
Why is it? (or I don’t understand something maybe)

It is based on AP (Army Points) not number of squads\units.

AP also includes heroes and equipment.

So if you have 1000 AP, 300 of that must be Inf/Archers

Oh. I understood. Thank you for your quick answer.

You're welcome