The 80% volume is a legacy fix for Windows 8. We found loud volume levels distorted much easier in Windows 8 compared with Windows 7. DPS is detecting Windows 10 as Windows 8 so the 80% volume fix is applied.
All of these volume problems are corrected in DPS 2.0. We have included a new look-ahead peak limiter to prevent any distortion at any volume level. DPS 2.0 is now set for release in October.