There is another option if the length of the cord and attached fabric is to be reduced to 1/3rd.

You can make the folds equal by tying the cord to whatever holds it at measured intervals, and include a small loop at one end of the pleated part.

To pleat, pull the first length of cord through the loop, so making a second loop, pull the next length of cord through the new loop, repeat along the pleats. At the end of the pleats tie the last loop to the end of the cord or pass the byter end through the last loop.

If you leave the ends of the cord long enough so you can tie it to your waist and so support the weight of the pleats, it should make the adjusting and arranging of the rest of the fabric easier.