Issue with outline size using sprite tiles

Hi. I'm making a game that uses 13x13 tiles and the borders of the level have the same type of tiles but with an outline. These tiles are 2x the scale on Unity.

My problem is that the outline does not have the same size on the entire level despite the sprites having the same size. You can see in the following image that size diference despite being the same sprites. The top hole isn't supposed to have an outline so that's how it's supposed to look!

I'm not using any Unity add-ons or anything like that. The tiles are a simple sprite, nothing fancy happening here. I also, have anti-aliasing and texture filtering disabled since that was causing artifacts in the edges of the sprites.

Do I have any wrong setting selected or something like that? Does anyone have similar issues? Any help would be appreciated, thanks!