Lyra output gain 10db less than expected

[Smaug]

I was wondering why my custom-built soundfonts sounded so quiet in Lyra, so built a simple SFZ with a single sine wave at maximum amplitude (0dBFS):

<region>
sample=Test Tone 1000Hz 0dB 10s.wav
lokey=1 hikey=127
pitch_keycenter=60
lovel=0 hivel=127
pan=0
volume=0

Playing this back in Lyra at velocity=127 and CC07=127 produces an output at -10dBFS with all faders at 0dB. It seems that Lyra has a hard-wired 10dB headroom. Why is that? I don't think this is part of the SFZ spec. In comparison the Plogue Sforzando AU plugin plays this at full volume in Logic.