Ok, that’s a bit of a corner case, but I can see how it would be useful in such cases. However, having multiple grids that you are able to move between would require changes to both Pathfinding and Find Tiles in Range, which would for every tile checked also make sure there might be any tiles that can be moved to/seen outside the bounds of the current grid. This would in the very least require some new branches.
This might not seem like that big of a deal, but every new addition to those very heavy function means a measurable slowing in the calculations. Even though this would probably not be noticeable to the user I would personally prefer map building to be a bit more awkward compared to making pathfinding less efficient if I was to make a T-map.