Effective in "Terrain" and Archer Comparison (6.2 RC/RR)

[Fotchimus]

Two questions:

1. What exactly does say "Effective in Deserts" do? Beyond the obvious, I mean what does it do for a unit's stats?

2. As Egypt I have access to two decent foot archers: Nubian Archers and the later tier Desert Archers. At a glance it appears Nubian Archers are superior because they have 5 missile attack to the 4 missile attack of Desert Archers. Both have long range missiles. So from a purely ranged combat standpoint, it seems the more easily accessable Nubian Archers are better than the more "advanced" Desert Archers. Is this true or am I missing some hidden values the Desert Archers might have?

[asn]

RRRC uses an AOR system of recruitment, with regional units being available in later tiers, even if they're not as good as the ones you would normally get. So while you could recruit nubian archers anywhere, the desert archers are locals pressed into service, etc, and can only be recruited in desert regions.
As the Fatmids, you know that you have better archers anyway, but if you're playing as the Byzantines, for example, whose only good archers are also AOR, this opens a new reserve of moderately effective troops.

IIRC, "effective in deserts" means that they have a lower heat value and don't tire as fast as knights (or any other heavily armoured unit) would in hot conditions