Yes, I was taught how to fold my tubular spares in 1964 (60-year-old habit ) , so I'm well aware of the technique. But, as you may or may not know, that method has nothing to do with protecting the inner surface of the tire from the valve stem and everything to do with keeping the tread on the outer side of the folds, to avoid folding the tread back on itself and thus risk the formation of cracks in the tread (edit: or, come to think of it, they might have also wanted to avoid breaking carcass threads in delicate handmade tubulars).

Folding the tube exactly as manufacturers fold it (with the valve nestled between the tube folds) works perfectly. And why not keep the valve cap on? You avoid the possibility, however remote, of abrading the tube with the pointy end of the Presta valve.