According to the manual, for setstyleext
setstyleext( stylename, fontsize, styleproperty, fontcolor, fontratio )
fontsize, styleproperty, fontcolor and fontratio will take a value of -1 to mean that no change from the base style is required. This works for all the parameters except fontratio.

Setting fontratio to -1 produces the correct display in the designer, but in print preview and output via Image the text squashed to what looks like a font ratio of -1.