nope its not essential. i fixed it.
- fritzing uses the viewbox attribute of the svg to scale the parts. i put the viewbox to “0 0 21.7 16.2” which is the exact size of the part on the pcb view. this let me use the mm values in the svg
- the text had fontsize once in the style and once in an attribute. according to svg spec the one in the css is used if provided, and the other ignored. just seems that fritzings export goes haywire when both are provided. i deleted the font size in the style and it now does export correctly.