Tactics now are locate the good areas with the large X35 coil and then move down to the small Elliptical HF coil using 17 Hz,with high reactivity to get through all the mineralisation and occupation contamination.
For any number people out there came it at a very steady 75 .
Rightly or wrongly as mentioned previously I am a number man using notch programs for coin shooting. Knowing this particular site now for a couple of years I know that Roman coins come in between 70 and 90 around 95% of the time ( bronze to silver.) Not sure what gold would come in at though since I have never found one..... yet !!
Lower than 70 the coins are usually grots or fragments. All the excellent quality ones have for sure without exception all come in around that 75 number I think because of their condition , shape and thickness.
Lesson to be noted is forget what people say or you see on the internet, just set up your machine to suit your personal preferences and the site you are searching .