-
I think that sadly the invisible line is also permeable to ethnic groups, which is why Turkey may have been keen to exploit that 'tiny cut corner' that you describe - they are keen to defend the Turkmen people living in that area.
Whether that is a sensible decision is of course another matter - and tbh there don't seem to be many sensible decisions - or indeed options - coming out of that particular shit-show right now.
One pilot is dead, shit is extremely real.
The Russian jet essentially cut a tiny corner on an invisible border, I know the Russians generally don't give many fucks about stepping on toes but I do not understand who thought that shooting this jet down was a good idea.