The vertical orientation of the aerial produces a completely different effect, because the flux linking the core falls sharply to zero as it reaches the same position directly above the conductor.
This ‘null’ signal is easier to detect than a ‘maximum’ signal position, so a vertical aerial would seem to pinpoint a line with greater precision. However, it is more prone to interference and therefore less accurate than a peak locate.
However, it gives no indication of line direction, so is much less suited to normal location and tracing duties. It can be useful for cross checking accuracy when pinpointing with a horizontal aerial instrument.