Well, still a Construct noob myself, but are you sure that this isn't the typical tile problem which is the reason tiles are often set up with "smeared pixels" around the actually used pixels so the GPU doesn't render blank space if resizing the tiles?
In GameMaker this is a common problem even documented on the official YoYo page:
(Sorry for a link to the "competition".. but the article seems to be fitting here..)
https://docs.yoyogames.com/source/dadio ... tiles.html
I think I've read somewhere that construct takes care for this problem itself.. but who nows.....