From what I read (and who know if it is correct) the Encore went like this
Deep Concave Original Design - Was changed because people where crushing pellets and getting erratic velocity
Flat face, Second Design - Did not result in people crushing pellets but made the crud ring more pronounced
Concave with Small Flat Area, third design - Helped with crud ring and kept pellets from getting crushed
If that is correct, it looks liked they started with the second Encore plug design for the Pro Hunter instead of going straight to the third design.