I've been digging through the abi_base.gda file, making a few adjustments to various skills, but one item I haven't been able to determine presently is what category, if any, will increase the radius of a specific ability (I'm particularly looking at some of the Warrior buffs and and aggro-drawing ones). Anybody know which column that is? I tried to use Taunt as my guideline; since it has a 10 Diameter by default, 16 with upgrade, it should be easy to spot if it's there, but I didn't spot it. However, given how janky the numeric values are in the various .uti files, I haven't ruled out the possibility that maybe the numbers aren't entirely straightforward.
I managed to find it, just posting the answer here for anyone who tries to find it in the future: Ability diameters are not in abi_base.gda, they're in a separate file, persistent.gda. Most use the same ability ID across both files though in a few cases, an ability ID code for a different skill is filled in the aoe_primary column of abi_base.gda which is then used as a reference point in persistent.gda (so for example, I put the Ability ID for Battle Synergy into the aoe_primary column for Rally, then increased said diameter in persistent.gda, and in-game, the diameter for both increased).
Also, one rather interesting thing I discovered in this is that changing an Ability's diameter in persistent.gda will not be seen by the game unless you quit and relaunch the entire game. However, changes to abi_base.gda are visible immediately upon loading a save, without a need to relaunch the whole game. But since you can flag abilities to match others in abi_base.gda, you can still, theoretically, change ability diameters without relaunching by matching them to another ability.