Assessing ship conflicts in complex inland waterways is challenging because constrained navigation environments and heterogeneous ship interactions limit the applicability of generic safety thresholds. This study proposes a behavior-informed conflict assessment method using AIS data. AIS trajectories are first processed to detect candidate maneuvers from heading and speed variations. Geometry-induced turning behavior is then filtered using waterway spatial constraints, and the remaining maneuvers are associated with crossing and overtaking encounters to identify avoidance-onset samples. These samples are used to optimize the parameters of encounter-specific ship-domain models, thereby linking domain construction directly to observed navigator behavior. Empirical analysis of AIS data from the Taicang reach of the Yangtze River yielded 10,256 valid ship trajectories. Passenger vessels and tugboats were excluded because their operating patterns differ from those of merchant vessels. Based on the optimized domains, ship conflicts were identified and quantified through domain overlap. Spatial analysis identified two descriptive concentration regions associated with crossing conflicts, while overtaking conflicts showed a more continuous distribution along the main channel. These patterns provide interpretable evidence for targeted inland-waterway safety management.