Ketsueki, I couldnt tell you how far my thumb extends out when holding the pick, simply because, I dont pay that much attention to it. Really, (this is probably not "textbook" advice , but ) I just hold it however it feels comfortable. The only problem Ive ever had is having the pick slip outta my hand when doing fast (alternate) picking. To remedy that, as obvious as it may sound, I just hold the pick tighter! Sorry if this doesnt help much... rock on!!