The problem isn't the footprint, it's the deco slots.
In TS4 for some ridiculously odd reason, the developers thought it would be a good idea to make slots in different sizes and objects categorized according to slotting behavior. In previous games, anything that could snap to a slot .... could snap to ANY slot, there was none of this asinine size/category requirements for objects.
In TS4, If an object is categorized as:
0 - will not sit on a surface (which is what floor plants are categorized as, regardless of their size)
1 - will sit in small, medium, and large slots
2 - will sit in medium and large slots
3 - will sit in large slots only
Surfaces have different types of slots, in S4S they are represented by cylinders in different colors for the different slot sizes.
All base game shelves have only small deco slots, so only objects that are categorized as a "1" will snap to those slots
https://i.imgur.com/PX7wCnu.png
In S4S, you can tell an object's slot category
https://i.imgur.com/bPbjxGm.png
TVs need a special slot on surfaces for them to snap, because of needing to be repaired.
https://i.imgur.com/5rS0Y76.png
