Hmmm.
On the missing ST point: I'd agree if they missed last season having held one for, say, the previous 5 years. I wouldn't agree if they missed the first season at the AMEX and have held one for the other 5 seasons (ie they want to have 180 LP as a starting point). I'm not sure about those who missed, say, season 3 at the AMEX. What is your solution for these people? Or season 4? Or season 2? You see the issue?
Current system for consecutive seasons:
1 season - 50
2 seasons - 90
3 seasons - 120
4 seasons - 150
5 seasons - 170
I would just say 4/5 = 150 points, 3/5 seasons = 120, 2/5 = 90 and 1/5 = 50, regardless of whether or not they were held in consecutive years.