All you need to know about getting your model scale correct.
Many new 3ds Max users have problems with the scale of their exported models not matching the scale in the Max UI. Here are some tips on solving that.
Understanding Displacement Blend Texture Scale
This page explains one cause for displacement materials to be scaled incorrectly in Source as well as the solution. You should use bitmaps of equal dimensions in both materials controlling the Blend material.
Fixed in VMF Exporter 1.21 (WWMT 1.768)
The current VMF Exporter does not yet export the correct texture alignment, rotation and scaling on brush geometry and displacements.
The Wall Worm Material Library Generator originally created DirectX Materials for all materials. But updates to the VMF Exporter changed the way materials are interpretted. Whenever possible, you should not use DirectX Materials.