Selecting tiles in an isometric tileset

Hey! My goal is to make a building system in my 2d isometric grid, right now I'm working on making a selection box appear in the tile of the object you're selecting. I use Unity's tilemaps and tiles for the blocks.

The problem is that when hovering over certain parts of a block, tiles next to it get selected even though the cursor is visually on top of the same block. My goal is to select the tile of the block where the mouse cursor is visually on.

As an example, if your mouse is hovering at the location marked with a pink crosshair, I'd want the light green tile to be selected since the object you're hovering over is still the grass block with the blue lines. However, what is actually happening is that the brown tile gets selected. I have made a video hoping that it would clear up some confusion. Currently I'm using a tilemap collider and a raycast that gets sent from the mouse position to the blocks. How could I implement this? In case it helps, I have matrixes of the different layers of the grid.

https://vimeo.com/1080354185/15e6227475?ts=0&share=copy
Video of my issue

https://preview.redd.it/23ys8te9d1ye1.png?width=644&format=png&auto=webp&s=278d11b9b3c58145fb1f7686f89deef2dbf4039d






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