What's the mechanic of the Impi Spear Throw?

[MKDELTA3]

So I've been thinking of making a mod where the ranged mounted units wouldn't be tru ranged units but would have a ranged first strike like the Zulu Impis.

Apparently what gives the Impis their ranged first strike is the following somewhat cryptic promotion:

Spoiler :

-<Row>

<Type>PROMOTION_ANTI_GUNPOWDER</Type>

<Description>TXT_KEY_PROMOTION_ANTI_GUNPOWDER</Description>

<Help>TXT_KEY_PROMOTION_ANTI_GUNPOWDER_HELP</Help>

<Sound>AS2D_IF_LEVELUP</Sound>

<PortraitIndex>9</PortraitIndex>

<IconAtlas>EXPANSION2_PROMOTION_ATLAS</IconAtlas>

<PediaType>PEDIA_ATTRIBUTES</PediaType>

<PediaEntry>TXT_KEY_PROMOTION_ANTI_GUNPOWDER</PediaEntry>

<CannotBeChosen>true</CannotBeChosen>

<RangedSupportFire>true</RangedSupportFire>

<LostWithUpgrade>true</LostWithUpgrade>

</Row>

The true meat and bones of the first strike appears to be the <RangedSupportFire> tag, but it has no numeric value, only true. So how does the game determine the strenght of the attack? I haven't played the Zulus that much but from what I remember it seemed to be notably less than the melee attack. But is it some fixed value ( ) or a percentage of combat strenght or what?