Different validation mAP when finetuning RFDETR Nano with resolution=320 vs resolution=640 despite possible silent fallback to 384

I fine-tuned two models from RFDETRNano using rfdetr 1.6.4, once with resolution=320 and once with resolution=640. from my understanding, version 1.6.4 silently ignores unsupported resolutions and falls back to 384 during training. If that is the case, I would expect both training runs to produce identical validation metrics, yet I observe markedly different EMA mAP values: resolution=320 → best EMA mAP reaches 0.2560 by epoch 4 resolution=640 → best EMA mAP reaches 0.3192 by epoch 4 Full logs: RFDETR Nano with resolution=320 [2026-04-27 15:12:41] [INFO] rf-detr - Best EMA mAP improved to 0.0014 (epoch 0) [2026-04-27 15:14:07] [INFO] rf-detr - Best regular mAP saved to /kaggle/working/checkpoint_best_regular.pth [2026-04-27 15:14:07] [INFO] rf-detr - Best EMA mAP improved to 0.0267 (epoch 0) [2026-04-27 15:16:25] [INFO] rf-detr - Best regular mAP saved to /kaggle/working/checkpoint_best_regular.pth (epoch 1) [2026-04-27 15:16:26] [INFO] rf-detr - Best EMA mAP improved to 0.0829 (epoch 1) [2026-04-27 15:19:03] [INFO] rf-detr - Best regular mAP saved to /kaggle/working/checkpoint_best_regular.pth (epoch 2) [2026-04-27 15:19:03] [INFO] rf-detr - Best EMA mAP improved to 0.1474 (epoch 2) [2026-04-27 15:21:43] [INFO] rf-detr - Best regular mAP saved to /kaggle/working/checkpoint_best_regular.pth (epoch 3) [2026-04-27 15:21:43] [INFO] rf-detr - Best EMA mAP improved to 0.2030 (epoch 3) [2026-04-27 15:24:29] [INFO] rf-detr - Best regular mAP saved to /kaggle/working/checkpoint_best_regular.pth (epoch 4) [2026-04-27 15:24:29] [INFO] rf-detr - Best EMA mAP improved to 0.2560 (epoch 4) RFDETR Nano with resolution=640 [2026-04-27 15:33:26] [INFO] rf-detr - Best EMA mAP improved to 0.0006 (epoch 0) [2026-04-27 15:36:13] [INFO] rf-detr - Best regular mAP saved to /kaggle/working/checkpoint_best_regular.pth (epoch 0) [2026-04-27 15:36:13] [INFO] rf-detr - Best EMA mAP improved to 0.0490 (epoch 0) [2026-04-27 15:39:45] [INFO] rf-detr - Best regular mAP saved to /kaggle/working/checkpoint_best_regular.pth (epoch 1) [2026-04-27 15:39:45] [INFO] rf-detr - Best EMA mAP improved to 0.1600 (epoch 1) [2026-04-27 15:43:48] [INFO] rf-detr - Best regular mAP saved to /kaggle/working/checkpoint_best_regular.pth (epoch 2) [2026-04-27 15:43:48] [INFO] rf-detr - Best EMA mAP improved to 0.2631 (epoch 2) [2026-04-27 15:47:53] [INFO] rf-detr - Best regular mAP saved to /kaggle/working/checkpoint_best_regular.pth (epoch 3) [2026-04-27 15:47:54] [INFO] rf-detr - Best EMA mAP improved to 0.2928 (epoch 3) [2026-04-27 15:51:47] [INFO] rf-detr - Best regular mAP saved to /kaggle/working/checkpoint_best_regular.pth (epoch 4) [2026-04-27 15:51:48] [INFO] rf-detr - Best EMA mAP improved to 0.3192 (epoch 4)