Additionally, the record head is used to introduce a tape bias signal that improves frequency response.
Additionally, the heads are arranged so the combination of the two signals results in a small "dead zone" directly past the recording head where high frequency signals are blanked out.
This prevents subsequent high frequency signals from interfering with those just recorded, by the time they exit the dead zone they are too far from the head to be overwritten.
One was the need to keep the heads in proper alignment, which was tricky for the average user.
For proper results, cross-field recording needed high quality tapes, to ensure the oxide layer was thick enough to allow the bias signal to imprint on the deeper levels of the oxide without reaching the front surface.