Best way to add short rows to lengthen the back of a top?

Hi,

I’ve heard of adding short rows to the back of a sweater to lengthen it. What’s the best way to do this? Is there a rule of thumb for how many rows to do and the way to shape them?

It’s usually done at the neck or upper part between the shoulders. I think you only need a few rows, maybe 4-8.

I don’t think it is to lengthen the back exactly but to bring the back neck up so that it fits better. And it may help keep it from riding up in front like sweaters do sometimes.