There are two distinct types of alpaca, the Suri and the Huacaya with distinct types of fiber.
Most of the alpaca fiber you can get is from the Huacaya. The Huacaya fleece should have a bit of a crimp and have a strong staple definition.
The Suri fleece will be straight with little to no crimp, their fiber is longer than the Huacaya.
Each animal, even in the same breed, can produce a different type of fiber. Genetics play a major role, as does care and feed of the animal. also color plays a role. Darker colors are generally courser than lighter colors.
4" is a fine staple to work with.