Foster, who was riding a Ducati 999 with a number of modifications, had done five practice runs and three competition runs over the two days of the event.
He failed to negotiate a right-hand bend and his motorcycle left the road and hit a wire farm fence, Senior Constable Glenn Marshall said.
It is estimated Foster was travelling at 178km/h when he crashed.
Waugh, who was riding a triumph Daytona 675, could have been travelling between 188 and 218km/h when he crashed, Marshall said.
The course does not have barriers providing protection to the riders the same way a dedicated racing course would.
Waugh failed to negotiate a bend, left the road, and hit the wire fence.
Marshall said a witness statement mentioned there were five road cones placed just before the corner, but they might have been moved after Waugh's crash to block the road.
He believed the cones were there to alert riders to the fact they were approaching a dangerous corner.
They had all earlier been briefed on the cones.
Marshall said the course itself was a dangerous one, particularly as there was "no run off at all" and no room for error.
He said a strainer on the fence was unusually placed, as it was outside the fence line.
There was another post further around the corner that Foster would have hit if he continued his arc, Marshall said.
The fence has now been modified and the fence line shifted back.
Marshall believed the crashes were caused by both rider error and the nature of the course.
Looking at the lines both men took through the corner and their respective speeds, Marshall thought there was no way to avoid injury.
"There was no way they were going to come out of those corners without significant injury."
He also said it was possible Foster had hit a bird, as feathers were found embedded in his kill switch.
There was no evidence he swerved, however.
Former President of Motorcycle NZ Jim Tuckerman agreed with coroner Ryan's statement that "very experienced riders can make slight errors resulting in tragic outcomes".
"You can be a hundred mils out in the road and that's the difference between being in the fence and not being in the fence, it's literally the blink of an eye," Tuckerman said.
He said riders needed to slow down.
"Racing motorcyclists tend to have a knob on the side of their helmet that turns the throttle on and common sense off."
Tuckerman did not believe there was any feasible option to make the course safer except to push back the fence line and move the hazardous fence post, which had already been done.
"I honestly don't think anything could have been done to prevent either accident.
"It's down to the rider against the course."
