I think a 1oz shot and 3oz of milk is just about perfect, for me.
Of course it depends on the coffee and how I want to pull it but as a general statement I like a 1 & 3 combo. Maybe a punchy coffee at .75oz would work but I think it would be a bit under-volume for my palate. Not that it would be bad or wrong, it would just be something less than what I like.
Most of the drinks in Sugar Land HQ were a 1 & 3 combo John, so that's gotta say something.