(One, you're trying to hit a target roughly a mile off with a spell using only your mind. Assuming you used the most accurate method, which would be to use the existing connection to funnel the spell to the target, you would likely exhaust all your personal energy simply pushing that one spell. Also, since the eye is at the other end of it, you would have to push the spell though it too, thus killing it in a shower of gore. All other methods would have zero chance to hit.)
((Ahem. No. There are more ways than that. Like, say, finding the endpoint via a detect magic, then casting the spell so that the effects are already sent to the right coordinates of its own accord, and also A) Significant energy optimizations courtesy magic computer + regular computer + notes from the creation of the aforesaid magic computer/AI, B) Mana capacitors, C) No, spell cost does not scale with distance, should one do it right, D) Any spell that leaks effects like that, is stupid, and I would not cast it, E) Plenty of methods to disconnect the spell from the eye, F) Aforementioned magic computer can bloody well provide extra computational and thus casting capacity as it is also hooked up to my head, G) I don't need to push it along, if it's got a trail to track, I can just cast it and let it go, even if I wasn't doing other things...I really doubt that I can't hit the apparatus that you're using with this. If that's your brain, well.))
==Section From A Textbook==
"Casting at a distance is not, inherently, harder than any other spell. It is not the distance that is the problem, it is the fact that most spells rely on relative coordinates, or mental abstractions that involve a projectile traveling from point A to point B. Both of these are flaws in spellwork for anything but close combat applications, where frankly one does not have the time to set coordinates. It is much more effective to pick a reference point, and cast in an absolute coordinate system relative to that point. For instance, depending upon the application, one might choose the gate of a fortress, the engine room of a spaceship, or the core of a planet. Why, though, do we do this? Because doing so..."
==Complex Math About Inertial Frames Of Reference, and How Ambient Thaumic Fields Work, Boiling Down To The Result That A Person That Considers Themself To Be A Moving Object Ends Up Retranslating The Spell To The Frame Of Reference That They Consider Themself To Be In, Causing Thaumic And Computational Overhead Despite Not Actually Needing To Do So==
"So as you can see..."
==End Of Excerpt==