Why small and not large

[Jeep explorer]

Ok pretty critical title. Can someone explain why a pi detector that hits on small sub gram nuggets will miss plus 1 oz nuggets ? At depth? I would think that if your pi machine can id a .05 gram nugget it would find 1 oz larger nugget. At deeper depths. I am so confused

[waltr]

Which PI detector?
Coil?
Settings?
Testing conditions?

I have bench tested my HH2 PI with sub gram to 12gram nuggets and only difference is distance.