Abstract Appearance of an overcompensated positive electric field in most vertical field measurements performed very close to the channel core (0.1 m from it) is explained using the extended generalized traveling current source (extended GTCS) return stroke model with current reflections from the ground. As suggested by experiments in triggered lightning conditions or in measurements of simulated return strokes in the laboratory we assumed that the ground reflection coefficient depends on the current magnitude. New effects in the corona sheath due to the reflection of current pulses have been noted and taken into account. We separated the channel-base current into two components. The first current component is fast and with a greater peak value, while the second component is slower and with a lower peak. We analyzed two return strokes with simultaneously measured channel-base currents and close electric waveforms. In the first analyzed case, the first current component, with a peak value of over 15 kA, reflects from a perfect ground with the reflection coefficient that equals unity, while the second current component, with a peak value below 15 kA, reflects with the reflection coefficient lower than 1. In the second analyzed case, both current components reflect from the ground with the reflection coefficient