> You're right in saying that 2/3 and 3/2 are the right numbers to ensure that the population wealth stays the same.
Quick correction:
The article uses 0.6 and 1.5. In this setting, the population wealth increases and the wealth of almost any individual decreases.
In the comment you replied to, they propose 0.66 and 1.5. In this setting, the population wealth doesn't stay the same, it increases even more than before.
(In order for population wealth to stay the same, the payoffs should be 0.5 and 1.5)