An accumulator assembly for an agricultural harvester includes an accumulator configured to receive agricultural product from a header of the agricultural harvester via an inlet portion of the accumulator. The accumulator includes a front wall, a rear wall, and a floor. The accumulator assembly also includes at least one auger disposed within the accumulator and extending laterally across the accumulator. Furthermore, the accumulator assembly includes multiple conveying rollers positioned at a bottom of the accumulator, in which the conveying rollers are configured to convey the agricultural product toward a conveying system. A ratio of a maximum longitudinal extent of the accumulator between the front wall and the rear wall along a longitudinal axis of the accumulator assembly to a maximum vertical extent of the accumulator between a top of the inlet portion and the floor along a vertical axis of the accumulator assembly is greater than 0.8:1.