Aren't tricep dips done in a seated position with your hands on a bench behind you?

These are definitely chest dips as they are a replacement for the push up which is a chest/shoulder/arm assistance exercise.
How to Perform Dips with Proper Technique wrote:Not Locking the Elbows. Lock your elbows at the top. Squeeze your triceps & keep your chest up.
Shoulder Issues. Don’t go too low. Stop when you break parallel, keep your chest up & torso upright. Try shoulder dislocations.
Torso Pain. Don’t let your shoulders roll forward & don’t let your torso shift forward too much. Keep your chest up.
Mehdi talks about not letting the torso shift forward and keeping the chest up, so that would suggest to me that you need to keep as upright as possible. He also says chest up at lock out, so I would assume you'd return to vertical if you have shifted forward a little on the way down.