I recently tried to create a tree diagram using box drawing characters. Everything seemed fine, except for three characters which were misbehaving 😞. U+257{1,2,3} specifically. They should stretch from the corners of the 'box'. In fira code they look ... stunted.

Below I have a screenshot of the same diagram, first with Souce Code Pro, then with Fira Code.

If this could be rectified, that would be great!