Systems and methods for determining optimal water capacity or distribution for each of a plurality of sections of a field to be irrigated by an ancillary span of an irrigation system are provided. A path is determined for a steering tower of the ancillary span that is comprised of a plurality of position-based coordinates. The position of the ancillary span steering tower (and thus the position of the ancillary span) relative to the determined path is always known and, accordingly, the optimal water capacity or distribution for the needs of its location can be readily determined based upon a calculated area factor percentage.
