Double attack threshold (Path of Radiance)

As commonplace in Fire Emblem Games, a unit in Path of Radiance attacks twice if the difference between its speed and the enemy's speed reaches a threshold. Fire Emblem Wiki states that this threshold is 4.

In Chapter 15, I have the following Marcia (speed = 22)

trying to attack Muarim (speed = 18).

Even though she reached the threshold (4), she won't attack twice. Why?

She won't attack twice because her weapon is heavy enough to slow down her Attack Speed.

Attack Speed is based on Speed, but whenever a character uses a weapon with a Weight larger than their Strength, their Attack Speed is lowered by the difference.

Laguz Lances have a Weight of 17, which exceeds your Marcia's Strength by 2. Therefore, although her Speed is 22, her Attack Speed while wielding one is 20.

Claws have a Weight of 1 so Muarim with his 23 Strength here is not slowed down at all from his weapon, but the -1 on his speed from the Demi Band leaves his Attack Speed at 17.

Neither Attack Speed exceeds the other by 4, so no double attack occurs on either side.

https://fireemblemwiki.org/wiki/Attack_speed