so, now you can set the text height to what you want in the dimension style. if your dimensions are in model space you should set the fit setting for the dimension style to the inverse of your plot scale (ie, 200 for a 1:200 plot scale) then set your text height within the dimension style to the actual plotted height (ie, 1/8). when you make changes to the dimension style the dimensions that are using that style will automatically update.