Actually, let me explain proportionality via hypothetical murder scenarios

In example 2, however, shooting at the trespassers could be the proportional thing to do. A group of people is attacking a single person with weapons, so more defence force is acceptable. You have not really clarified anything because you have provided one disproportional situation where you agree with limits to self-defence, and one proportional example where you agree with an expansion. What would be disproportional however is if the homeowner follows these people as they go home, and kills them in their sleep. Surely, I suspect you do not believe that to be just, so once again you would likely agree with a proportional response.