Standard storage boxes are very large, especially compared to train wagons. This mod attempts to make them more realistic. Wood, iron, and steel boxes are updated to 1, 2, and 3 slots, or 1/16 the original size. Logistics chests are 4 slots, so that logistics storage isn't quite as awkward. Train wagons are 14 slots, or 1/3 the original size (rounded up).
The real purpose here was to reduce the times you need to limit storage chests (since they're all pretty limited now), and to make it necessary to make longer and more realistic trains to carry the resources your factory needs.