Compare the SEF DD and the 6½" Concentric against each other ON THE SAME DETECTOR. Not SEF on MXT All-Pro and 6½" on the V3i as the detectors work differently. Use both coils on the same detectors. Better info, too, as you can compare the DD vs Concentric on the V3i, which is super-digital designed, and the DD and Concentric on the MXT All-Pro which has more of an analog/digital blend behavior to it.
Use the same naturally located target [size=small](not a plant)[/size] and work both detectors with both coil across the target from the same position and sweep direction prior to target recovery. Take a note pad to log your results, then share them with folks here on the MXT Users Forum.
Thanks,
Monte