How to scale a mesh properly?

So I have been recently trying to learn stuff, bit by bit to get into modding more.

And im currently trying to rescale three vanilla grass meshes so their sizes would be either 0.7 or 0.5 scale compared to original.

Meshes being: tundragrass01 tundragrassobj03 tundragrassobj04

So while I do manage to scale the meshes "somewhat" properly im hitting a brick wall, because im doing it wrong.. and the grass in question starts flying 20metres from the ground.

Im using Nifskope, And edited manually the BSTriShape on corresponding meshes. Tho the minor information that I could gather on the subject was: "Right-click the preview" -> "Transform -> Scale Vertices" ( My NifSkope does not have for some reason the latter option availeble on the Transform part )

Do I need to use creation kit for this? Or how do I do this properly in NifSkope so the grass does not try to fly into Sovngarde ? Sorry for silly post and questions :( Any guides/pointers/help would be appreciated

Also I know there is a mod for 50% vanilla grass availeble, but I was looking around and it adds awful lot of Vertices and Triangles compared to vanilla meshes. Scaling should not cause that right?