Jon,
The Heli side only has 1 and 2 for linear, and then 6 for curve. You don't have 3, 4, or 5, as they are used up giving your standard heli features. Rather than call your mixes 1,2,3 and have confusion about whether 3 was a curve or not a curve, they used the same layout and nomenclature as the aircraft side and called them 1, 2, 6.