I'm sure Kane is right about the weigtht and all of that but for shoulder health I would recommend sticking to torso slightly leaned forward and hands slightly forward of body.
I honestly don't look at dips like a "tri" exercise. If I want just a tri exercise I'd just do some type of heavy extensions, etc..
The difference being is that dips being a closed chain movement with the distal end fixed, if you look at it like "tris" or "chest" or "delts" you are missing the point that you can't move one joint without significant movment in another. And therefore there are positions that are healthier and not as healthy.
Whereas with a tri extension you can work the elbow extensors without necessarily putting your shoulders in a vulnerable position.
Obviously I'm not saying dips are not a tremendous tri developer. I'm saying that the way you think about an exercise drives the way you perform it and that can affect just how long you will be able to perform is safely. Dips are very effective in position I described. It's progression that matters anyway. You don't sacrifice anything when you get to keep your shoulders (potentially)
