Casting spells within a Dominion aura reduces casting totals, but what about spells cast outside the aura that enter the aura? For example, what happens when casting Leap of Homecoming to an arcane connection that is located in a far off city with a Dominion aura, but the magus casting it is standing inside a magic aura? Which aura do you use?
I’m sure you use the aura of where you are when the spell is cast.
Not even an ongoing effect with Penetration is affected by moving into another Aura. However the MR if the target is. This is why the tricks of the Intangible Assassin works so well, when cast from a high aura prepared space, at a target in a hostile aura.
I believe you use the Aura interaction from where you actually cast the spell, not where you end up, even if you use Arcane Tunnels and the like; from your comfy 3 Covenant Magic aura into a horrid 5 Church Dominion Aura, you have that placid +3 and no particular botch penalty.
Targets on the other side aligned with the Aura in that side may have Magic Resistance, and higher than usual, because of the Aura, though.
*edited Welp, Christian Andersen has higher Quik than I!