Depending on how you use Siri throughout your workflow, you might find a new free jailbreak tweak called AutoDismissSiri by iOS developer Andreas Henriksson to be an advantageous supplement to your jailbroken handset.
Just as the tweak’s name implies, AutoDismissSiri adds a timeout period to the Siri interface. That said, if Siri would idle on your device for a specific amount of time, then the interface closes automatically.