You're still referring to fire based upon direct observation in line of sight. They just got up higher so that they could see further. Indirect fire, which really permits the extension of the gun's useful range, is dependent upon an FO system, which the technology of the time generally did not permit. One might have used flags, or for pre-planned fires one might have strung wire and used the telegraph, but the problem was also conceptual. No one had really done it before.