Is (getvar "textsize") what you need instead of dimscale? You also have to ensure the text style used does not have a predefined height.
From F1 help for textsize:
Sets the default height for new text objects drawn with the current text style.
TEXTSIZE has no effect if the current text style has a fixed height.
-edit- if you just want the height to be 2.0, enter "2.0" instead of Height in your (command... ) line. Right now it is setting the value of Height to 2 times the current dimscale.