Here's the text on emanations from the Giantslayer AP to clear some of this up. I personally prefer using this rule, as it makes more sense to me.
"Bursts and Emanations and Larger Creatures
Source AP91
The rules often assume that creatures are Medium or Small. In the case of a handful of spells or effects with areas that feature a “radius emanation centered on you” such as antimagic field, aura of doom, and zone of silence, as well as some of the spells presented in this section, this can result in an area that is effectively useless when coming from a Large or larger caster. As an optional rule, when a creature casts an emanation or burst spell with the text “centered on you,” treat the creature’s entire space as the spell’s point of origin, and measure the spell’s area or effect from the edge of the creature’s space. For instance, an antimagic field cast by a fire giant would extend 10 feet beyond his space (effectively increasing the emanation’s radius by 5 feet)."