If the drain stops there meaning this is the higher side of the drain? The land might be different and he may be paying a different price, u need to refer to SnP to learn about the difference.

Floor plan not same?

Btw u can put rack there and extra space is always good

Spandrel were like that, mayb u can box up the lower area so it look more square and less awkward, but that also means wasting that narrow space which u can't do much anyway.

Maybe can hack wall and open up the space to join with the Spandrel as long it doesn't affect the stair support.