This paper proposes Exponentially Weighted Instance-Aware Repeat Factor Sampling (E-IRFS), an improvement on existing sampling-based rebalancing strategies (RFS, IRFS) to address the class imbalance problem commonly encountered in object detection models. E-IRFS uses exponential weighting, which applies an exponential function to the geometric mean of image and instance frequencies, to better reflect the differences between rare and frequent classes. Experiments conducted on the Fireman-UAV-RGBT dataset and four other publicly available datasets, using the YOLOv11 model, show that E-IRFS improves rare class detection performance by 22% compared to existing methods, particularly on lightweight models with limited capacity. This contributes to improving rare object detection performance in resource-constrained environments and demonstrates its suitability for real-time applications such as UAV-based emergency monitoring. The source code is available on GitHub.