That is a very long and interesting read. I will have to come back to it... didn't get as far as the back chaining dog...
So I guess mine is frustrated not fearful? Tho she's really not nice to the trigger dog if I let her off the lead... And I think some of the behaviour was her trying to get food off me. Now I don't use food in this situation - pay with pats and ear rubs and praise - she's much better. But still goes off if she's surprised (and I didn't see it coming ie when someone sneaks up on us (changes their direction to approach us).
It must be so confusing for other dog walkers - here is my dog with a group of other dogs - often small and fluffy, getting along fine with them... and their dog cannot join in.
Interestingly - I keep my dog on lead - and all the little dogs go off and harass the approaching dog. But my dog has taken to nipping and making the other dog squeal (tho some squeal when no contact is made)... So the little dogs are not setting a good example for mine Mine wants to "help".