I expect the answer to this one may involve the phrase 'use engineering judgement'. Anyhow heres the result of a little test on stress range for a 90degree bend:

1. use output from buried modeller directly:121MPa
2. add mid-nodes to above:142MPa
3. pre-divide bend into 4 tangent points before burial (don't add mid nodes):136MPa

So I guess I would tend to go with mid-nodes based on that outcome.