Tried in this order when the first marginal evaluation is not finite. They
are not a refinement of one another, and the ladder is not a search for a
better default: over eight families and five seeds the number of fits
reaching a converged solution is not monotone in frac, no value
dominates, and the spread between families is far larger than the spread
across frac. What the measurements support is that no single value
serves, so the point of the ladder is coverage.
Details
Ordered by that table: the two that did best on count, then 0.001 last, because it converges most often and misses the optimum most often – a start that clamped leaves the smooth pinned near its null space.
See .init_pars() for what frac means, dev/NOTES-sigma-frac.md for the
measurements and dev/bench-sigma-frac.R to reproduce them.