So, in my process of designing humanoid/humanesque sapient aliens, I often find myself wanting to have a species which are orthostatic (upright) bipeds like humans but which nonetheless have long tails, however, I do understand that the primary use of tails (balance) would not be applicable to an upright creature. The most obvious way to explain the retention of a tail would be to say that is is prehensile (as in many monkeys) or acts as a third leg (as in kangaroos), and some would simply give up and give them a raptorial posture, but I have come up with a new idea.
Essentially, my hypothesis is as follows: A ringed tail can be used as a defensive mechanism by means of tricking predators into attacking it rather than more vital body parts (or so I understand), and, if this is true, raptoriality would not evolve in a creature with a ringed tail, because then the tail would be too vital to be used as a diversion in a raptorial case, and so, if a creature's tail were ringed it would evolve to be orthostatic, in this way retaining a tail in orthostasis without prehensility. In short, a ringed tail could be a valid defence mechanism even if it were not prehensile and even in combination with an orthostatic posture, and would, in many cases, be mutually exclusive with a raptorial posture.
Is the above hypothesis correct? Or is there a flaw or omission in my reasoning?