Muscle tone is the tension of the muscle assumed caused by the motor nerve activity. For this reason we talk e.g. about a tone at rest which mean the tension when no action by the muscle is undertaken. The tone in general is as far as I am concerned a bit more complicated since e.g. tension of the fascia could contribute to the rest tone. Also to consider that tone is depending on the activity of the nerve which innervates the muscle. In case of hightened stress physical or mental the nerve activity will go up.
Positioning of a joint can also alter nerve activity by propriocepsis feedback.
What I have tried to do is not to answer your question but to direct you in a couple of directions which will help you to understand tone. Thus look into what nerves assist in feedback to the muscle ( muscle length/tension and propriocepsis) and you will find the answer.