With all due respect I can’t agree with you 100%. Yes, psychological factor is important due to our self esteem is very vulnerable for all those years of stuttering, especially it’s “inconsistency.” Still I belief that physiological reason is as much of importance. The thing is that we are very vulnerable to such speech characteristics as tempo, e. g. If your conversational partner sticks, most likely involuntarily, to your speech pattern, you feel more comfortable. My observation that more aggressive people don’t need to accommodate to your specific pattern. That makes your physiological response and subsequently speech to suffer. IMO psychology just follows it.