I think that you are grossly oversimplifying the transmission of power via an AC tranmission line. The bar voltage in the substations at both termination points of the line will depend on the electrical impedance characteristics of the conductors themselves as well as the quantity of power (real and reactive) being tranmsmitted.
I can't say that I've ever seen a situation where the voltage profile along a line is important, particularly a short line like the hypothetical 4-mile line mentioned. What would be of greater concern to me would be the bar conditions in each substation under various line loading scenarios, and whether or not these voltage tolerances are within those allowed by the applicable utility operational allowances and/or local grid code. The quality of service to the end consumer would be the factor of critical importance.
