here's the answer you need :
If you are using the Firestorm viewer, the answer is easy. Just use the Height Offset slider in your Quick Preferences menu. If you are using another viewer, you can do the same thing by adjusting the AvatarZOffset debug setting in Advanced (CTRL+Alt+D) >>> Debug Settings. You'll probably get frustrated, though, because you'll probably only need the Z-offset in a few sims, so you'll need to keep adjusting it in those few places where you need it.
Hmm i just looked it up but this option is no longer in firestorm
the only solution is to wear them shoe attachments and experiment till you get to the right height