i guess the way to determine the ratio is to make sure it has a direct relationship to the verdict,
for example (a fabricated one), if their is a case about a drunk man who is 2.5 over the bac limit and assaulted someone and is arguing that it was the bartenders fault for serving him too much alcohol. If the judge says a person can under no circumstances be held responsible for their actions if they are drunk and a bac of 2.9 is certainly considered drunk. the man is then found to be not guilty, then the ratio of the case is what the judge said about resposibility. if he said other stuff like questioning the bartender about why the man was served so much alcohol and saying that the bartender should have been more responsible, then i think thats obiter