Moustache

Hi there, I assembled the board, placed it in a casing have an original Tesoro Lobo Coil, used a carbon monopod as rod and a grip from an angular grinder. The problem I have is is there a description on how to fine-tune the pots etc.? It works, but detect coins and my white-gold ring at only 5-10cm distance trough air... In some description I have from the original Lobo it should detect these things at about 12 inches (30 cm).. Anyone who knows where to start and what the procedure is?