Sagiro
Rodent of Uncertain Parentage
Uller said:
Heck...I wouldn't even require a save in most cases(edit: when the target knows what is being cast and has readied an action to deal with it)...if they can reasonably reach the edge with a weapon or something, they can disrupt the spell automatically, IMO.
Hmmm. I don't think this would work, for the same reason that a person can't effectively ready the action "When I see that wizard casting fireball, I run 30 feet to the left." I mean, they can, but since the wizard goes after the ready-er, said wizard can just re-aim the fireball.
In the same way, a wizard casting wall of force would notice that a foe is sticking an arm out, and adjust the final location of the spell accordingly.
And that doesn't even address the other difficulties that the "targetted" character will have -- he doesn't know where the wall of force will be centered, or what its radius will be. It would still be a guess (with a small chance of accuracy) as to where exactly the wall will form.
At least, that's how I see it.
-Sagiro