Morkus from Orkus
The point, though, is whether or not that warband will also be looking out for fireballs behind every tree. As the game assumes that spellcasters are relatively few in number, the answer will be no unless the DM changes things for his world.How big of an issue is a wizard/fireball going to be to an actual army? Even targeted at the optimal spot, assuming 1 orc every 5 ft you're talking 40-some orcs. If it's literally an army, that wizard just took out 1% or less of an army that is now going to destroy the caster. The range isn't really all that long.
As far as an orcish war band, I never assume they're organized enough to march in formation. But it will vary depending on campaign, situation and leadership.