What makes for a “proper” soundstage for Symphonic music?

A follow up to a previously thread with various answers.
It was pointed out that different conductors use different instrument placement.
But I consistently hear the same “standard” placement.
Violins on the left front and violas and cellos on the right front.
Basses and brass on the right back.
Woodwinds on the right to center middle.
Percussion on the left back.
Harp on the left middle.