The separation between MEASURED, ESTIMATED, and INTERPOLATED results gives the 57-run dataset a clearer scope. For the predictive layer, I would add a grouped holdout alongside the held-out configurations you describe: reserve an entire model size or precision/backend combination, then compare its error with ordinary configuration-level validation.
Nearby context lengths from the same model can make a split look reassuring without testing whether the predictor handles a genuinely new regime. Reporting those two errors separately would help users judge a recommendation outside the measured grid. A clear 'outside coverage' signal would also prevent a precise-looking prediction from implying stronger evidence than the dataset supplies.