The annoying doorway jutting out of W.Hills has probably been disturbing the flow of people for over a 100 years, and you have to wonder why the road planners did not buy the now site of W.Hills when they set out the course of Dartmouth Rd as it is now. There had to be something important there that they wanted to preserve.

My thoughts are that there was a short lived half section of decorative canal preserved on this side of the road on this site, that matched the half section of canal that was bricked in along Davids Rd - too many angles of the W.Hill site align a little too well - this is by design imo.
I'll speculate further and suggest that there was some original canal feature jutting out at this point, like the wall of the swing bridge. Merging old maps can put a canal wall aligned right under this very doorway.

No evidence for any of this though. I try to be interesting...