If I were a 4th level worker at your company implementing some important but invisible part of the core product, and suddenly the kicker pool rewards me with a couple of million, I might seriously consider quitting. Who wants to be a middle class salaryman in (pretty shitty) San Francisco when they could be a comfortable upper class person in almost everywhere else in the world?
Imagine running Facebook, and 50% of your 3200 employees suddenly earns $2M (for perhaps 2 years of work). How will your company suffer if even 10% of those immediately quit their jobs?
That looks like a possible catastrophe to me. A simple solution would be to make the kicker pool a bonus pool that just pays out the due amount linearly over 5 years. No one will be thinking of leaving if they're going to be paid a bonus that's 3 times their salary for the next 5 years.