Is this all a version of the 'coffin curve' ?
Do you mean "coffin corner"? That is the term used for the high-altitude situation, achievable by some jets, where you are at the low-speed (i.e. 1.0g) stall
and the limiting mach (and the associated buffet and shock-induced stall) at the same time. The term was used by, I think, B-47 crews who got into that situation and found it very difficult to escape it.