Fully mechanized top coal caving (FMTC) is a primary modern coal mining technique, and its efficiency and safety are crucial for coal production efficiency. To clarify the top coal crushing mechanism and boost recovery rates, this paper establishes a mechanical model of top coal under static load in extra - thick coal seams. The model combines fracture mechanics, the pseudo-force method, and the maximum circumferential stress theory. By introducing the coal discharge port wide d, based on numerical simulation, d was corrected, and a more precise migration equation for the top coal caving body in the inclination direction was derived, the migration equation of the top coal caving body in the dip direction was derived. the migration equation of the top coal discharge body in the dip direction is derived. The discrete element method models irregular particle clusters, and Python-based released-body inversion analyzes the fully developed released - body morphology and coal-gangue boundary. Results indicate that at crack angles of 0° and 54.25°, crack propagation stress becomes infinite, decoupling coal fragmentation from crack propagation. As the shield beam angle increases, the upward release body width and semi-arc length decrease, as does coal release efficiency. The right coal-gangue boundary shifts closer to the goaf with a larger shield beam angle. For coal release quantity and efficiency, a shield beam angle of 30° with one-step coal release per mining step is optimal. With more coal discharge ports, the release body’s long-to-short axis ratio and eccentricity decrease, and its shape transitions from a vertical ellipse to a near-circle. The maximum curvature on both sides of the coal - gangue boundary occurs near the boundary. Under dual-port coal release, the top coal recovery rate peaks at 88.23% but with the lowest release efficiency. Adding discharge ports reduces recovery by 2.58% and 2.03% under triple-and quad-port conditions. Meanwhile, coal discharge efficiency rises remarkably with more discharge ports, increasing by 41.96% and 18.01% for each additional port. Overall, this study on irregular particle clusters reveals top coal migration laws, offering theoretical and technical support for safe mining and top coal recovery enhancement.