Large Custom Entities' inventories don't stay open when riding

Custom entities in add-ons, if very large and the rider’s seat placed high up, auto-close their inventory if a rider attempts to open, meaning there is no way to access the inventory. Increasing the mob’s hitbox to encompass the seating area sometimes helps but there is a point at which this no longer works.

Ideally the inventory will open regardless of the player's location or mob size.