Here is what we currently use:
Mid: The ability to regenerate from decapitation or severe brain damage. For machines and vehicles, this would be regenerating from the destruction of critical parts, such as the engine.
High-Mid: The ability to regenerate from being blown / cut to pieces, or from a small piece of the user's body, such as a severed head, a single organ, or a finger.
Low-High: The ability to regenerate from having no solid parts of the body remaining. This can range from a puddle or drop of blood to even a single cell. For robots and machines, this can also include regenerating from a liquid state.
And here is what I want us to use:
Mid: The ability to regenerate from decapitation or severe brain damage. For machines and vehicles, this would be regenerating from the destruction of critical parts, such as the engine.
High-Mid: The ability to regenerate from being blown/cut to pieces, brain included, or from a small piece of the user's body, such as a finger, or the heart.
Low-High: The ability to regenerate from having no solid parts of the body remaining. This can range from a puddle or drop of blood to even a single cell. For robots and machines, this can also include regenerating from a liquid state.
As you can see, there is a much more logical progression of severity in this manner.