Anita Phillips has criticised the ''one size fits all'' approach of the proposed secure unit after the government on Monday published its draft model of care for the 25-bed facility.

Ms Phillips described the range of patients the government hoped to accommodate in the Symonston facility as ''quite extreme'' and ''inappropriate''.

She said the territory needed separate, smaller facilities for different types of patients in need of secure mental health care.

But the government has defended the plan and said it was not practical or possible to fragment patients into separate units in a jurisdiction as small as the ACT.

The medium secure unit, which has suffered years of delays, is due to be built by the end of 2016.

Under the government's proposal, patients that could be housed in the unit include patients who have committed crimes and a range of patients who do not need to be in a correctional setting but require secure mental health care.

The unit will be split into 10 acute and 15 rehabilitation beds.

The government said on Monday that the facility would ''respond to the needs of people with mental illness who are or are likely to become involved with the criminal justice system, and for others who cannot be treated in a less restrictive environment''.

Ms Phillips said the facility was expected to hold patients who would transfer back into the community or a correctional setting depending on their circumstances, alongside long-term patients.

She added that the ''clearest issue was in terms of gender'' because the unit was intended for both men and women.

''There will be men and women, old and young, they're all too different to be just put into the same one-size-fits-all facility,'' she said.

''They're looking at people who can be rehabilitated, people with drug and alcohol issues, people who have committed crime and may be there a short time and then go back to jail.''

Ms Phillips' predecessor, Heather McGregor, warned against ''bundling'' patients into a single secure facility nearly 10 years ago.

''The range of the people who might be accommodated there is quite extreme,'' Ms Phillips said.

''I don't believe it will work.''

Chief Minister Katy Gallagher said the plan was open for consultation and encouraged those with an interest in the model ''to engage constructively with the consultation process''.

''This consultation process is designed to provide an opportunity for all those with an interest to put forward their views for consideration by the government before a final model of care is announced in 2014,'' she said.

''However, it will not be practical, efficient or possible to fragment a highly specialised service into a number of even smaller services to support the low level of people requiring this service.''