I believe that this is correct Patrick, and Ascorbate also loses its ability to cross oxidize. Therefore it cannot work as an ET developer or in a superadditive manner as pH goes down.
This is why I wondered what the sulfite did to pH in your previous post. If pH went up, likely the activity of ascorbate would increase (IIRC, you used ascorbate. I am sorry but I didn't look at that post to refresh my memory).
In any event, ascorbic acid is pH sensitive as you describe.