I have a question regarding tuning. If a 7 string is in drop A tuning it's AEADGBE. So why is it AEADF#B for drop A tuning on a 6 string? Why F# instead of G?
Because it's based on standard 6-string tuning, same intervals as EADGBE. So standard B tuning is BEADF#B, F# is the major third in that tuning as B is on E standard. While a 7 string just adds another string with the lower 4th (B) to the existing E standard.