Other troubles the can occur when using this method are highlighted below.
With the waist just beneath the bust, it doesn't have anything to keep it from sliding down your body as the day wears on.
Fabric becomes trapped under the child's bottom or hangs way over the waistband making either a poor seat or an overly deep seat.
Because of the fabric lost under the bottom, the back of the carrier does not come as high on the child as it could. The wearer also may not be able to tighten the straps sufficiently. This mother has the straps as tight as they will go and wants them tighter.
Contrast the same child worn with the same carrier at her mother's waist.
The child has a much better seat, she has support all the way up her back, and her mother can get a much tighter fit with her straps. You can also see the child feels more confident and supported in the carry because in the earlier photo she was holding on to her mother, whereas she has relaxed in this carry.
Does this mean that if you have a buckle carrier that you like wearing under the bust we saying your must stop? No, of course not. But if you ask us to show you how to use an SSC on your back, we will not demonstrate a high back carry. And if you come asking for a carrier to do a high back carry, we will recommend a mei tai or wrap as carriers better suited to the task. There are a few buckle carriers with unstructured waists if you really want a higher back carry and buckles, but they still may not fit your body because of the tightening issue mentioned with the straps. Hopefully this illustrates more clearly the pitfalls of this popular recommendation.