Dividing a Peony

Yes, the chatter was about herbaceous Peonies; its their tubers that like to sunbathe .

I don't know the drill for Tree Peonies, but it would not surprise me at all, being grafted, to hear that "plant deep" is correct advice. They don't have tubers, so the advice about Herbaceous Peonies does not apply, so unless there is some other reason to shallow plant them I reckon you are fine.