There doesn't appear to be a stop on the Parkhurst clip, like other stripper clips.  It appears to me that it just barely went in the slot, with perhaps the bevel on the front of the rear slot catching the spring of the clip, which some clips I've found images of, don't appear to have.  It looks as though the rear slot was meant to open the spring of the clip, or at least allow room for opening of it.  Now I see, thanks to OP's pic at just the right angle, it was made to open the spring of the clip and said spring has wings that would make for a positive stop.  A major redesign might be needed to make Enfield strippers work.  The ones I have are pretty stiff and require considerable force to get the rounds moving.  Steinmeyer device, I like that!