Truth - not sure exactly what you mean by disc 1 (is that the tone break for discrimination you are using, vice "0"?)
Anyway, Park 1 may not be the ideal mode for lead depth. It is a great mode for silver and high conductors because it is biased/weighted to the lower frequencies which hit harder on high conductors like pure copper and silver.
Minie balls ring up around 17 to 19 and are therefore considered mid-conductors (smaller lead objects like minie fragments and camp lead will read a little lower). Therefore, if you want to go deep on minies, then you may want to try one of the "2" modes either Park 2 or Field 2 because they are biased/weighted to the higher frequencies which hit harder on mid-conductors like brass, lead, nickel, gold, and, unfortunately, aluminum. You might give up a little depth on silver and copper by doing this, but you will not be shut out on silvers by any means. if you want to try a single frequency approach (I really do not recommend this because you lose a lot of the multiIQ advantages in terms of signal processing) pick any Park or Field mode and try running it at 20 khz or 40 khz to specifically target those mid conductors.
HTH