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But if there's enough in the reservoir to not pull in air under braking then more fluid won't make a difference, it'll just top up the reservoir which is still useful if there's room, as it'll need the fluid as the pads wear and the system self adjusts.
Either there's a bit of air in the system, in which case the "burping" process I described above should help (and top up the reservoir) or possibly you're not used to hydros just tending to have a bit more lever throw, you rarely actually pull them that hard, so give it a test ride and see.
This shouldn't really work. Or rather, without ninja level bleed tricks I don't understand why it would do anything.