Notalent is correct. The reason or basis of all this is first adjacent channel interference to KLVP Aloha on the lower sideband side where they have requested additional power from the default authorization of -14 dBc up to -10dBc. I don’t know where the -14dBc allowable is derived from (where in the rules, that is). To make it even more complicated, their signal northward would have to respect Canadian airspace. I have NFC what that entails for digital but we can assume that since it was OK in the analog domain, the digital hybrid signal is OK as well, and the additional power in the lower sideband still propagates no further than the analog signal.
Here is the first letter in the series of STAs which includes the report by Erik Swanson of Hatfield and Dawson and has the best explanation of the reason for the STA.