Even for a pulse induction metal detector, maximum depth is determined by the target, size, orientation, and soil conditions. PI metal detectors are known for their excellent depth detection, so they will outperform VLF machines especially in mineralized ground.
Small nuggets such as 1 g sizes can be found in 6” to 9” soils, but you could very well find them at deeper depths. Use the appropriate timings for the soil conditions to achieve maximum depth detection while taking into account all the other factors that affects detection on small targets.