The range of Charles' telepathy (it's actualy not one of Sophia's, it's a mutation in his brain.) Isn't definite, since it depends on several factors, such as his state of mind, the amount of concentration he's applying to it, ambient "noise" (such as concentrations of energy) and his target. In a general guess, with the flat landscape, lack of mana powered machinery, and Charles' current mindset, you can probably grab his attention from anywhere in the region.