It's actually much easier to work with twips since all forms sizes actually are specified in twips. The scalewidth and scaleheight can't be used to change the size of the form, but instead the scale of the form. You can also use

screen.twipsperpixelx and screen.twipsperpixely to get the ratio between pixels and twips. It's usually 15.

And you can use ScaleX and ScaleY methods to convert between any scalemodes