How each doctor performs injectables such as Botox (botulinum toxin) and fillers differ slightly, and it depends on the patient factors as well as the doctor's experience.
For jaw muscle relaxation to achieve facial slimming, there are a few variable patient factors: the size of the muscle, the current facial shape, the desired end result, any concurrent issues such as bruxism (teeth grinding), as well as previous treatment results.
Generally the larger the muscle, the more Botox is needed, and the more points of injection for the Botox to diffuse over the larger muscle. Generally, Botox spreads 1cm with the standard dilution, so patients with small muscles may indeed just require 1 injection point. Personally, I prefer to divide the Botox dosage evenly throughout the desired area of jaw reduction. I have even seen experienced physicians spread their injections over 5 points of more.
The patient's facial shape also influences the placement of the Botox injections. If there is already some hollowing seen below the zygomatic arch (cheek bone laterally), it would be preferable to place the injections lower down to avoid any further relative prominence of the zygomatic arches. Thus, placement of injection points, and not just dosage and number of injection points, is crucial.
Some patients tell me that they do not want too small a lower face as it makes them appear worse. On the other hand, some patients desire a very V-shaped lower face. Expectations of patients do influence the treatment protocols as well.
If the patient has bruxism, then dosage, and the number of injection points may need to be increased to cover the muscle area adequately.
Physician factors, such as the previous patients' results, do guide a doctor on how he/she adapts her injection techniques to best suit each individual.
See a doctor whom you trust, and is able to explain to you the rationale behind the decisions for his/her treatment.