It is correct that the CPF contribution is pegged at $6k income per month. Anything more than $6k pm will not attract CPF contribution. Meaning, a person with $20k pm salary will contribute the same amount to his CPF as the guy who earns $6k pm.

And the maximum salary that attracts CPF contribution per year is $6k x 17 months = $102K. At 37% CPF contribution rate (total of employee and employer contribution), the maximum a person (below 55 yo) can contribute to his CPF is 0.37 x $102,000 = $37,740. A person above 55 yo will only contribute 26% or $26,520 per year.

The 17 months is to allow bonuses and other cash benefits a person earns to attract CPF contributions both from the employee and the employer. So if a person happens to earn $6k a month and has 5 months of bonus in that year, he will be contributing $37,740 for the year. If he earns more than that, his CPF contribution will still be capped at $37,740.

There are many ways to increase your contributions or savings into your CPF. You can look them up in the CPF website