It has been previously shown using computational modelling of a 50th percentile adult seated in a commercial wheelchair that the occupant pelvic‐belt angle with respect to the horizontal should be between 45°‐60° to reduce pelvic loading and prevent submarining, instead of 30°‐75° as recommended by voluntary ISO standards. This paper extends the previous work by using computational modelling to evaluate the influence of combined shoulder‐belt and pelvic‐belt position on a 5th percentile female, a 50th percentile male and a 95th percentile male occupant to study kinematics and loading in a standardized 20g frontal impact. The belt configuration is more realistically represented. The results show that, for all dummy sizes, the horizontal component of the pelvic‐belt force remains broadly constant as the pelvic‐belt angle increases from 30°‐75°, but the vertical pelvic‐belt force triples. A critical belt angle of around 45° was identified, below which predicted abdomen loading, pelvis rotation and head/neck injury risks are increased. The shoulder‐belt force increased with pelvic‐belt angle. Moreover, pelvic‐belt angles higher than 60° greatly increased occupant excursions, abdomen loading and head/neck/chest injury risks. These results again indicate an optimum pelvic‐belt angle in the region of 45°‐ 60°, depending on the occupant size.