The board shall establish standards for determining assessments when such assessments are less than the full cost of care. Such standards shall be based on the income, assets, and other circumstances of the persons liable for cost of care and shall include consideration of the number of dependents, as defined under Georgia income tax law and regulations; legal rights to payment under any insurance agreement, and other evidence of ability to pay; but no assessment shall be fixed or collected on the basis of any assets exempted by subsection (b) of Code Section 37-9-8. In determining assessments for persons liable for cost of care, the department shall develop procedures to ensure that no dependent, deduction, or personal exemption as defined by Georgia income tax law will be reflected more than once in the determination of assessments for any one patient. In establishing standards to determine such assessments, the board shall adopt criteria to be applied uniformly to all persons liable for cost of care, except that the board may adopt separate criteria for assessing monthly benefits or funds from any source to cover cost of care, support, and treatment provided to patients who are hospitalized for longer than three months and whose current needs, as defined by the Social Security Administration, are being met. However, the board shall ensure that the assessment made each month shall allow the recipients of such benefits or funds to retain at a minimum an amount as a personal allowance equal to the amount of the personal needs allowance allowed beneficiaries under the state medical assistance plan. Further, such standards will include special provisions for assessing mentally retarded respite care admissions under Code Section 37-4-21 or any other respite program allowed by law or duly adopted departmental regulations, where such admissions are legally limited to 56 days of care a year. To the extent practicable, such criteria shall ensure that persons having the same or substantially the same financial ability to pay cost of care shall have the same or substantially the same financial obligation to pay such cost of care.