you are able to defend yourself with a degree of force one level above the level of the threat
Fallacy mate, the law surrounding self defense says that a person may defend them self using a force that is reasonable, and proportionate to the threat (or very similar words) and goes on to say that the force can be applied to subdue that threat and prevent its reasonably foreseeable recurrence.
There are a number of myths around self defense, the one up rule, the reflex response........all crapola.
The other dilemma is that reasonable and proportionate are not defined specifically in the acts, they are determined by the circumstances in each case, according to the reasonable person test............would a reasonable person conclude your actions unavoidable and justifiable.
The other keystone to self defense is having no other choice, if withdrawal is an option, rather than pounding your attacker into the pavement/drawing a gun etc, then the law would expect you to withdraw and show a willingness to not fight, the defense of "self defense" comes into play when you have no other option.
I am neither a police officer or lawyer, I have taught self defense for 20 years, and have instructed a number of professional groups, mostly in healthcare on the legal framework for self defense and how to respond to aggression and violence.
If I have any of this R-sup I am sure one of the coppers or lawyers on here will correct me, but I am fairly confident that the basic principals I have outlined are accurate.