Suppose the PCs had said, "It's messy and potentially dangerous to attack the vampire head-on. Let's go to the Lake of Optalis, where all sight is particularly enhanced. From there, we'll scry upon Garrett and teleport right to him, neatly circumventing his defenses."
I would have thought that was the bees' knees. I would have bounced in my chair excitedly at the thought of the PCs making the arcane geography of the land work for them. (I was terribly pleased when Monica figured out Garrett's whereabouts from the prophecy.)
As it is, though (and this is why I mention this publicly), there's no reason for the party to go to Optalis. Prolix can already scry anything under the rules as I've established them, so there's no reason to try to improve his far-sight.
I'm inclined to tweak things so that this becomes a good idea, and I may well do so--though I don't want to do so by outright changing the rules I've established.