I might be wrong, but I read "corner" as the corners around shop doors and such. Some would be shallow (a shop door just a couple of feet inside the wall), while others would be deep (alleys, or shop doors sunken further, where someone could more easily hide and evade an angled side-eye glance).Yeah, that’s the 101, what I was initially taught. Reactionary gaps I learned about later.
What do you define as a “deep corner”?