Around 3 no higher then 4 ever.I wish I could tell more,anything above 4 and it will sound off just from swinging it.With my c$ I can get that light tone and I know its deep.With the 3D I have never had a light tone,they all have been the same on deep or on top of the ground.I dont think theres a problem.Just where I hunt,all over the state.I mostly hit park,not knowing people or the area it hard to find old sites to hunt,I never hunt unless I ask.I pass by so many old farms that are falling down and wish I could hunt it,just dont know who to ask.So all I ever get is parks that have been hit by every person around.I did get to talk to a farmer one day and he told me I could hunt this old house, just havent been back down there.I may only be in the area a day and then move on.I had a 12in coil on my MXT and had to run sen low with it too.Is it just the large coil?