Question: Why no XftFontMatch?

I'm studying the differences between st-sx and st-flexipatch. I noticed st-sx does not use the `USE_XFTFONTMATCH_PATCH` and I wonder why. In my comparative tests, I can't see any font size rendering difference between st-flexipatch with the patch, and st-sx without. Does st-sx skip the patch for some reason? If so, what is the reason? My test runs two systems each with a primary monitor only; the monitors have different size and pixel size. I test `Monospace:size=13` and `Monospace:pixelsize=13`. The st window for the `size` case is larger than the `pixelsize` window (as expected). The `size` case yields different window sizes between the monitors (as expected); so does the `pixelsize` (as expected). I wonder what is the benefit of this patch. Perhaps I should test a single system with two monitors (primary and secondary) to see some benefit. Unfortunately, neither of my systems has dual monitor ports. Thank you for your comments.