The rule of thumb is that a lead Region of a multi-regional civil action is determined by where the complaint and conclusion are filed. Multi-regional cases are usually civil judicial cases. It can be administrative but is rare.
If the multi-regional enforcement action is a bankruptcy action the the lead region is decided on a case-by-case basis. Most bankruptcy actions are filed in either the federal of New York or Delaware so Regions 2 and 3 would unfairly receive the lead a disproportionate amount of the time. Current law says companies can file for bankruptcy where they are incorporated. Many companies are incorporated in Delaware, in part because of favorable tax law.