Some heights and fan-canon for my series LongTale/LongFell.
So in LongFell/LongTale once Sans gets out and begins enjoying life on the overground, without noticing he “grows up” along with Frisk.
I like the fancanon that Sans is actually a skeleton of one of the 7 children, along with Papyrus. Reading up on child development I came across Failure to Thrive, it’s when a child in early life suffers from either sever abuse/depression/anxiety will have their growth stunted. Shortening their height, weakening their health, Frisk suffers an amount of this while Sans greatly. Even tho Sans is a grown monster mentally his body is stuck in time as a child.
Until, magically though happiness, content and LOVE his skeleton and health begin to grow. As said before he nor Frisk noticed, they grew about the same rate so didn’t notice the difference in height. Neither did anyone else til Alpyhs noticed the catch up in height.
Expected in Frisk the human but no one though Sans would gain height as well so late in his life, he still a shorty but it just shows progress and improvement in his new life.