In my experience over the years of ponying lots of youngsters about, I'd say
if the rope can get under Gabe's tail you have the pony lead way to long. I
give enough length to allow the ponied horse to go straight, i.e. not
crooking it's neck towards me, and insist that the head stay by my knee.
Also, NEVER, ever, dally around a saddle horn or tie it off to you, saddle
or other horse. Keep the rope in your hand which means you hold reins to
horse you are riding in other hand. I manage to have it in my hand so if
ponied horse pulls away it gets a bit of freedom but I still have another
piece of the rope in my hand so it doesn't get totally away from me. If the
ponied horse has enough length to get the lead under Gabe's tail it is long
enough to get around your body and create a very dangerous situation.