Don't know what an SSA is. But I've seen flat/gently-increasing payout curves over 4 years, ~250k each.

I worked at MS for 3 years after undergrad, My first year was 221k, 180k, 191k and would've been ~185k for Y4 then 160k after cliff.

SSA is Special Stock Award given arbitrarily (M2s are not sure or have any say in who/how much to be given) but believed to be used for retention by HR. Annual stock refreshers for <L63 at Microsoft are in the range of 0-20k vesting over 5 years.

I chose to move to Amazon then recently Apple.