Because when we tested out the early versions of Bravura on humans, back when I had to hack its glyphs into Sibelius because we hadn’t yet progressed sufficiently far with Dorico itself to use it to print out music, we tried out a number of different variations for notehead size, and the consensus was that an enlargement of around 7–8% was considered most legible at standard reading distances. That’s therefore why we use the enlarged noteheads by default. However, technically the SMuFL standard stipulates that noteheads should be exactly one space tall, so our preferred noteheads are actually out of spec. So we call the ones that are sized according to the SMuFL specification “default”, and the ones that are sized according to our real-world tests for legibility “larger”, and we choose the more legible ones by default.