[BHaType]

You can try to use this

https://developer.valvesoftware.com/...lisionProperty
CCollisionProperty::SetSurroundingBoundsType( SurroundingBoundsType_t, Vector const*, Vector const*)

or this

https://developer.valvesoftware.com/wiki/Bounding_box
UTIL_SetSize() or CBaseEntity::SetSize()