The Leg-Insertion Ippon-Seoi-Nage is sometimes referred to as the Split-Hip Ippon-Seoi-Nage as well. It is a very popular contest version of the standing ippon-seoi-nage.

The late, great Toshihiko Koga, arguably the best ippon-seoi-nage player ever, used this form of standing ippon-seoi.

The key factor here is inserting your lead leg (right leg if you are throwing to the right, left leg if throwing to the left) deep in between uke's legs. This allows you to get your belt line below uke's belt line without bending  your knees or squatting.

To understand why bending your knees during seoi-nage is a bad idea, see this posting.

The leg insertion (or split hip) takes some getting used to and many beginners have difficulty doing the turn and the lunge to achieve this technique but once you get it right, you will see how powerful it is.