There is a minimum range for carapace weapons. It would come into play with say enemy titans and units in larger buildings, etc.
From the main rule book:
Vehicles & Measuring Distances
There is however a notable exception, a vehicle's weaponry. When firing a vehicle's weapons, ranges are measured from the muzzle of the firing weapon, whilst line of sight is determined from the weapon's mounting point along it's barrel (as explained later).
Under the warlord entry:
Weapons mounted on the carapace of the Warlord have a minimum range of 24".
How it was wrong to interpret it according to this rule? (Serious question, not looking to start a flame war but when stating something is wrong about a rule, lets post the rule to counter the argument)
For the most part, playing by that rule would be fine from my perspective. (My perspective is from the table top a foot or so away from an Emperor's toes.) If you measure line of sight from the mounting point of the Black Emperor to the ground, there would be an effective minimum range of at least 36 inches in most directions. The body of the Black Emperor (and the Red Emperor as well) just gets in the way of shots aimed near the feet of the titan. If we had played by the above rule strictly, an awful lot of the shots targeting Dan and I would have been misses due to blocked line of sight.
I suspect the 36 inch minimum range in the rules for carapace weapons was intended to simulate this firing arc and line of sight problem simply. Also, if we were using, say, a string or laser to determine line of sight, and as players are scratch building their titans, it would be tempting for a scratch building player to mount carapace weapons way forward on the carapace so as to increase the coverage of the firing arc.
I would be inclined to keep the 36 inch rule rather than tempt scratch builders to improve their firing arcs or require tall step ladders so we can eyeball titan carapace lines of sight. I won't get emotional about the precise rule being used so long as the spirit of the 36 inch rule is kept, that carapace weapons aren't supposed to be able to shoot one's own toes, and that scratch builders copy the Forge World carapace designs with this in mind.
I'll also repeat a suggestion for a 45 degree down firing arc for carapace weapons. A warlord shooting at an Emperor shouldn't have a problem depressing weapons to hit its target. If a target is tall enough, it might be hit even if it is within 36 inches.
