Accurate non-destructive evaluation (NDE) of concrete compressive strength is critical for quality control and structural health monitoring. However, the inherent directionality of concrete properties due to casting, compaction, and curing poses a significant challenge to the reliability of single-orientation methods. This study investigates the directional sensitivity of non-destructive testing (NDT) methods for concrete strength assessment and develops orientation-specific empirical models for improved prediction accuracy. Experimental data from M25 concrete specimens were collected using rebound hammer tests in three perpendicular directions (downward, rightward, upward) combined with ultrasonic pulse velocity (UPV) measurements in three configurations (direct, semi-direct, indirect) across 7, 14, and 28 days of curing. Statistical analysis revealed significant directional variations in both rebound hammer readings and UPV measurements. Multivariate regression models incorporating UPV data and curing age explained 95.8%, 98.7%, and 96.3% of compressive strength variance for downward, rightward, and upward orientations respectively (p < 0.01). Validation with independent data confirmed high predictive accuracy (R²: 0.957-0.987, RMSE: 0.81-1.51 MPa). The rightward model demonstrated optimal performance (R² = 0.987), while all directional models significantly outperformed conventional single-orientation approaches. Results demonstrate that direction-sensitive modeling substantially enhances the reliability of non-destructive concrete strength assessment, particularly for in-situ quality control of existing structures.