I did as you described in the past, and now also use a set up similar to yours with the rope / prussic knot and carabiner attachment.
I think if you experiment with the placement of your rope with respect to the location of the loop you are feeding the end thru it might help.
If nothing else, carry a small twist tie ( they make heavier duty ones for camping etc) and place it around the loop thru which the tag end passes, after you did this, to snug up the loop and not allow it to droop at all. My system does not seem to have the same issues you describe in spite of my doing , seemingly, the very same as you.
ChuckC