📦 WP-093 — fix(losses): stable angle regression for elongated boxes¶
Research log · Phase 9 — Inference and generalization
🔗 Depends on WP-088 · Needed by none
WP-093 — stable angle regression for elongated boxes¶
The revised gain and its five-seed dose-response are A22. What lives here is the diagnosis, including the two mechanisms that were measured and ruled out — the part that would otherwise be lost, since a register records what was concluded and not what was eliminated.
Starting point: the oriented overfit gate cleared its 0.9 floor on 0 of 3 seeds at 100 epochs (mean 0.840) and 2 of 3 at 200 (mean 0.910, spread widened to 0.148). A longer budget is not the answer, and the widening spread says the problem is instability rather than under-training.
Measured per class, the shortfall is carried entirely by the one class whose AP depends on orientation:
| class | behaviour |
|---|---|
| square, circle | symmetry-protected: 0.93–0.99 AP while carrying 40–49° mean angular residuals |
| triangle | near-square (w/h 1.15), tolerant |
| rectangle (w/h 2.00) | tracks angle precision directly — carries the whole shortfall |
Two hypotheses were tested and rejected:
- A quarter-turn local minimum. Rectangle carries the least angular-error mass beyond 60° of any class. The 90° mass sits in square, where it is a true symmetry and costs nothing. The distribution is bimodal rather than gradual, which is what suggested a local minimum in the first place.
- Under-training. Seed 0 regressed from 0.8959 to 0.8177 when the budget was doubled.
Cause, found by paired five-seed ablation: R1 Eq. 15's angle term itself, at the 1.0 gain this project had assumed.
Two things the record deliberately does not do. It does not lower the floor to fit the measurement. And it does not claim a clean fix: the revised gain reaches 4 of 5 seeds, not 5 of 5 — seed 1 lands at 0.8638 with 19.84° error. Only dropping R1's angle term entirely reached 5 of 5, and that is a paper deviation the register does not authorise, since A22 is a gap R1 leaves open while the term itself is not.
The residual instability sits at 2:1 aspect ratios, which is the band where omega = 0.948 — a five percent reduction where R1's stated intent is that elongated boxes are "primarily constrained by the rotated IoU loss". At DOTA's 5:1 and 10:1 ratios omega genuinely falls (0.750, 0.555) and the term may behave as R1 intends. That remains unmeasured.