I can see how it increases volume if you are using ambience but it doesn't raise it above the dry piano volume.
The problem with this is trying to get a decent mix in midi if the piano is too quiet compared to the other instruments.
You can lower the volume on all instruments and raise the audio output level of your DAW but this could cause some problems.
Maybe it would be good to have a volume controller in the Aria player for midi work. Before rendering it to audio you could turn down the piano volume and once in audio you can increase the piano's amplitude to match the other instruments.