Can't help with sodium ascorbate, where I live its 4 times the price and certainly not as effective as ascorbic acid. And I do know from personal and others experience that at certain individual dose of pure ascorbic acid everyone runs to the toilet. Obviously that isn't the case with sodium asorbate.
Constipation actually was the only reason I got my father to take somewhat mega-dose ascorbic acid. Because a persistent constipation wasn't at all eased with pharmaceutical remedies, he finally and in his desperation got adventurous enough to try 1 teaspoon with a magnesium-rich Mineral-water (Rogaska Donat Mg). And continued to take that every second day since he still thinks having bowel-movement every day a bit too extreme..
Works for him like a charm, and has bowel-movements every second day.