The answer to the question has to do with the units used for font size in inkscape (this is not a problem with matlab). Inkscape uses 90dpi rendering while matlab and most other things use 72dpi. That means the inkscape will show the font size being 90/72 = 1.25 times bigger than the actual size. When printed, the actual size will still be 10pt, not 12.5 shown by inkscape. See myinkscape forum question for more details.
Also, I've decided using just the 'Position' property is the best way to go. I still set 'PaperPositionMode' to auto, though.
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