I have just checked the official CSA website and its says the following; - (has my edits)
The income of any partner living with the parent is
excluded from the calculation of net income.
However, a partner�s income can affect the allowance for children in exempt income (children living with the non resident parent) and can be taken into account in the first protected income calculation. Non-resident parents are not required to disclose their partner�s income, but if they do not, an interim maintenance assessment may be
imposed. BASICALLY you get a reduction in accountable income so you can provide for your children living with you but if the partners wage covers that it won't be taken into account. Does that make sense?