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Yup, 90º is the ideal and I've heard differing opinion on the line being through the pivot and cable mount and the pad/pad mount and cable mount.
Either way, while 90º might not be totally achievable on that VO brake, you could certainly do a lot better than it is in that photo.
@dangeek the brake arms are like a Touring but that cable set up is more like you would use on the wider armed Neo Retro.
(according to Jan Heine, who knows his stuff) the straddle cable has to be at a 90º angle with the straight line between the pivot and straddle mount on the canti.
Which is impossible on the above setup..