A system includes a gradient sensor arrangement deployed in a first borehole, the gradient sensor arrangement having a plurality of spaced sensors at a single measured depth position. The system also includes an electromagnetic (EM) transmitter deployed in a second borehole. The system also includes a processor configured to determine a distance or direction of the EM transmitter relative to the gradient sensor arrangement based on EM field measurements collected by the gradient sensor arrangement in response to an EM field emitted by the EM transmitter. The system also includes a directional drilling controller configured to update a trajectory for either the first borehole or the second borehole in response to the determined distance or direction.