>>sensitivity of Botox efficacy in migraine to the precise placement of the multiple injection points?
I wouldn't read too much into that claim of precise placement - could just be noise. Botox doesn't work on some people and does on others (there have been recent claims of a biomarker) and there is also a significant placebo effect here. So lots of noise in general.
Or it could be that you need to inject fairly close to the various branches of the trigeminal nerve.
Someday a brave neurologist will inject into a patient's sphenopalatine junction (at back of the nasal passage) and (I would predict) get great results.