i rarely have it cranked all the way up. i normally play with and adjust it
depending on the site and amount of trash and nearby interfering objects
if at a play ground or whatever.
thats a hard question to answer since soil conditions kind of dictate how high i can set it. ideally,i will crank it all the way up if i can,but if the machine starts to chatter and give false signals i will back it down untill it just becomes stable.
Every trip mine is maxed out. Also have the rest of the dfx maxed out accept for the block edit disc edit. I take -40 through plus 95. Anything else your running way to hot and will be digging iron 15 inches deep.