Is it possible for the hitboxes of certain items to be adjusted? (Maybe thats not what causes these issues but it was my best guess.)
There are some items that can be placed partially outside of your land - such as fences. This allows more freedom like being able to make connected fences around your adjacent plots of land. There are other items like Brick Flowerbeds and the Rose Arch with which you can do the same. Example attached - I've placed two Rose Arches between two of my land plots to create a tunnel between them.
Meanwhile other items are fully limited to where they can be placed - for example the new Rattan Pergola which has to be fully placed inside your land. With this being a large item, it limits the freedom you can have with it and it takes up excess farming space. Someone on discord also mentioned that some rugs can be placed under other items, while other rugs can't.
There worst part is there's no way to know without buying and trying but then you get stuck because most items are untradable. (And the rattan pack was hella expensive.)