Most decorations (signpost, flowers, crates...) occupy only one grid space(1x1) visually but they seem to be actually standard building size under the hood (2x2). This is usualy ok as they can partialy overlap, but it causes problems when you want to build decoration next to the building, it does not allow you to build to in the next grid spot because the decoration is 2x2 and it can't overlap with building.

There is also related problem that some of those small decorations have "pivot" in different place, meaning the visual part is in different square of the underlying 2x2 grid

maybe this will help illustrate my point (those are just examples, actual layout is probably different):

flower:
[ ] [ ]
[x] [ ]

crate:
[ ] [x]
[ ] [ ]

where [ ] is one square of the 2x2 grid that decorations use, [x] is actual place of the visual part of that decoration (stuff that you can actually see).

This causes problems when you want to place such decorations next to each other, you simply can't as they would occupy same 2x2 space.

Solution for both problems would be to make small decoration actually 1x1, not just visualy.