The credit is first applied to your tax liability and, depending on which education credit you are eligible for, may be reflected as a refund.
If the increase in your retirement income is producing an increase in your tax liability, more of the credit can be applied which would look as if the credit (tax break) is increasing.
In other words, as your increase your income, the education credit is not increasing; rather, since more credit can be applied to your higher tax liability, your tax break IS increasing.