By default, a destructable is 16 x 16. You can change the sizes of entities in the sprite editor, but when used as a destructable on the map, such as a large rock (32 x 32), its physical dimensions are always 16 x 16. This means that the hero will be standing on top of the large rock's edges in order to pick it up. So, without making a custom entity, could you maybe make an option in the entity dialogue box to change the collision dimensions?
Attached is an example of what I am talking about
Not possible yet. You need a custom entity.