Looks like the large mono coil and the smaller one are not too far off in air depth. PI's just don't work well in the air, they need a matrix to get a better reading. But, the large coil is light, covers more area, and add a little halo to the target, and it should be a killer. Because the size of the larger coil, it was picking up more electrical interference at lower threshold settings, so the results don't really justify greater depth with the smaller coil. The test was done in my living room. The tiniest target, however, the 22 lead bullet didn't fair so well with the larger coil, an expected result. But the air test did show that the higher the threshold setting, the deeper the target can be picked up.
Looking forward to your results next hunting season!