The top leg of the loop drops to hook over the bottom almost every time. Lefty Kreh has another explanation for tailing loops made by advanced casters. Casting tight loops by driving your rod in a straight-line path can also cause your trailing line to crash into the forward part of your loop. This happens with an extremely stiff wrist that locks the rod on one track. Let's fix or at least improve on our tailing loop dilemma.
Good casting is an oversimplified answer.
Practice a smooth application of the power stroke at all casting distances from short to long. Avoid any abrupt powering and stopping. It is also a big help to apply equal power to the front and rear. I call this fly fishing math. One plus one equals one.