# Insights (verified across nodes; each line cites the node)

- Full mixed-type tabular features plus log1p LightGBM beat a tiny numeric ridge on Ames because neighborhood/quality/area signals are sparse and nonlinear. [n001, score 0.1418]
- Monotone ordinal quality encodings (NA→0) let trees use quality gradients without treating Ex/Gd/TA as unordered labels. [n001, score 0.1418]
- TotalSF (basement+floors) dominated split gain over raw area proxies; Age/RemodAge also mattered. [n001, score 0.1418]
- Neighborhood one-hots plus ordinal quality/condition maps let a log-target linear model capture location and finish premia the 8-column ridge missed, cutting official RMSLE from 0.1836 to 0.14224. [n002, score 0.1422]
- Wide ~110-feature matrices need stronger Ridge regularization than alpha≤100; GCV sat on the cap until the grid was extended to 1–1000 (chosen ~200). [n002, score 0.1422]
- On this feature set ElasticNetCV ≈ Ridge (worker quick means 0.12966 vs 0.13125; l1_ratio stuck at 0.1), so L1 adds little once dummies are regularized. [n002, score 0.1422]
- Equal log-space averaging of three similar GBDTs can improve every quick fold yet shrink to a tiny holdout gain (official Δ=−0.00291), because the models’ residuals stay highly correlated. [n004, score 0.1389]
- The hardest quick fold barely moved (worker −0.00187), so complementary leaf/depth/cat biases alone do not fix Ames outlier houses. [n004, score 0.1389]
- Native CatBoost categoricals on Ames mixed fields plus TotalSF/Age and a log1p target cut official RMSLE from 0.1836 to 0.14379 versus size-only ridge because ordered target stats use neighborhood/quality the linear baseline never saw. [n003, score 0.1438]
- Worker quick-set moved the same way as validation (0.12187 vs ridge 0.16778), so the quick seed set tracked the official direction for this swap. [n003, score 0.1438]
- Training-only outlier drops can improve quick CV while hurting holdout if similar cheap palaces remain as prediction targets (quick −0.00235 vs official 0.14524 > parent 0.1389). [n005, score 0.1452]
- Aggregated bath/porch/quality×size features plus dropping zero-gain flags give only modest fold moves; they do not fix ~3× overprediction of cheap large homes when those rows stay in the eval set. [n005, score 0.1452]
- Partial log-residual correlation (~0.8) between a GBDT blend and Ridge means a 1/4 linear vote can help ordinary houses without delivering large mean RMSLE cuts. [n006, score 0.1369]
- Under equal weights, one fold where Ridge fails (high residual corr, weak alpha) can erase typical-fold gains and raise fold std. [n006, score 0.1369]
- CatBoost alone nearly matching the 3-tree blend implies weaker trees add little under equal averaging once a strong member dominates. [n006, score 0.1369]
- Train-only cheap-palace drops do not fix the same pattern at prediction time: Id 1299 stayed ~3× overpredicted when it was validation, so holdout twins can erase quick gains. [n007, score 0.1477]
- High train split gain for QualArea/TotalPorchSF did not translate to a clear official win versus parent 0.1418. [n007, score 0.1477]
- Inner OOF NNLS beating equal blend on train OOF does not imply outer gains: the 4-parameter simplex overfits correlated OOF columns and fails under train/predict shift. [n009, score 0.1368]
- A single global Ridge weight cannot handle both regimes: when the hard tail is held out, NNLS upweights Ridge on typical houses and hurts the held-out tail. [n009, score 0.1368]
- Living-area caps alone do not tame Ridge palace leverage when BsmtFinSF1 stays uncapped; Id 1299’s finished basement still drove ~1e6 preds until clipped to the TotalBsmtSF cap. [n008, score 0.1358]
- Dropping cheap/Edwards palaces from Ridge fit (not trees) improves other folds and luxury underprediction, but without predict-time caps fold-4 ridge stays ~0.17 when the palace is a target. [n008, score 0.1358]
- Equal-weight blend gains when Ridge stops casting a million-dollar vote even if trees still ~3–4× overpredict the cheap palace. [n008, score 0.1358]
- Cap finished-basement channels with TotalBsmtSF on palace rows: worker in-process showed uncapped BsmtFinSF1 as the largest log-price term on Id 1299. [n010, score 0.1367]
- Neighborhood/sale-condition-masked caps beat global ones: global p99 undercuts ordinary luxury; living-4000 alone left the palace fold high. [n010, score 0.1367]
- Do not drop train cheap-palaces when a held-out twin may appear: drop cannot fix folds that already hold the palace out and removes the only clipped training exemplar. [n010, score 0.1367]