TL;DRWhen reporting how many slots are used out of the number available in the item tooltip, take blocked slots into account, instead of reporting based solely on chest size.
What ?Item tooltips show chest availability, very handy especially when you are checking items from a distance: However, this can be misleading, if some (or all) of the container is blocked: Have the tool tip show that 4 out 4 slots are already used, or possibly 4 of 4 out of chest size 48.
Apply to all containers that support blocking, specifically and especially including train cargo wagons.
Why ?Less misleading: the current report suggests that 48-4=44 slots could still be filled, when in fact the chest is already "full."
More accurate information, better decisions.