Just had a quick look at the file, a couple of things. The stairs block at the bottom left, has a zero (or almost zero) length line in the block, which is causing the bounding box to be bigger on the right side. Editing the block and deleting the line will sort that out.
As for the rest, I wasn't sure which parts were causing problem, but if I go to Options menu - Advanced preferences and untick 'Geometric Select Edit', the bounding box is larger all the way round the object, Ticking 'Geometric Select Edit' the bounding box is tight to the objects.
However. With some of the objects, the bounding box vertex differs depending on the zoom level, zooming a long way in, is causing the bounding box to shift, and sorry, I've no idea why.