The three Ontario doctors, supported by the federal government, argued the inquest should focus only on the last days of Ashley Smith's life at the Grand Valley Institution in Kitchener, Ont., five years ago.
They argued Dr. John Carlisle's authority extended only to the Ontario border, and that he was barred from examining how federal prisons are run.
Smith's family, backed by other parties, wanted Carlisle to examine much more, including how Smith was treated at other prisons in other provinces long before her death.
"The challenge to the scope on constitutional grounds is anticipatory and premature," Carlisle ruled.
"I am aware of the limits imposed by the constitutional cases and will respect them."
Smith, 19, of Moncton, N.B., choked to death in October 2007 as guards essentially stood by. She spent most of her last year in solitary confinement exhibiting self-harming behaviours, and had been shunted 17 times among nine prisons in five provinces.
After shocking surveillance video of Smith was shown, correctional authorities withdrew their objections, and four out-of-province doctors agreed to appear as witnesses voluntarily.
Carlisle said he wanted to make his ruling anyway.
"I am being asked in the motion to consider a matter of jurisdiction, which cannot be acquired by consent or acquiescence," Carlisle wrote.
"I should thus consider all the arguments to determine if I have jurisdiction lest there be any doubt about the sufficiency of the opportunity to be fully heard by all parties."
Carlisle did make one minor change to the proposed scope of the probe to meet the objections raised.
Essentially, he made it clear he was mindful of the jurisdictional pitfalls, and wanted to be explicit he would not allow an unlimited examination of Correctional Service Canada.
"Smith happened to die in CSC care. By necessity, the inquest will inquire into the actions of CSC employees in their care of Ashley Smith while she was in its custody," he said.
"That is quite different from inquiring into the management of CSC."
As a result, among other things, the scope will look at the "challenges of providing mental health care to Ashley Smith" rather than to female inmates in general, Carlisle decided.
Overall, the inquest will delve into seven areas, among them the impact of prolonged and continuous segregation on Smith and the role of repeated transfers in light of her deteriorating mental health.
The inquest is slated to start hearing evidence in January.