IBOC and ssb or sync detection


I had a question concerning IBOC and sync: A strong signal (at least at my QTH in Laredo, TX) from an IBOC station (KRLD Dallas 1080 KHz) creates quite a bit of hash on 1070 and 1090. When using my Grundig G3 on 1070 (KNX Los Angeles), I was expecting to have less hash on the lower sideband or lower sideband sync than on the upper sideband (or upper sideband sync. Surprisingly (to me), the signal from 1070 was cleaner on upper sideband! When I checked for reception of a station on 1090, the LOWER sideband was cleaner! Why would this be?
An unrelated question or 2...The G3 holds sync, even on weak signals on upper sideband. On lower sideband, the set loses sync more easily (on weak signals). In the few days that I have had the set, it seems to be getting better at holding lower sideband sync. Is this possible? Could I be burning the set in and getting better results? I do have some local stations mix into sideband and sync reception...I can defeat this by touching the antenna base, or by deploying the atenuation switch. Could local mixing products result in sync working better on the upper sideband than lower? Sync or ECSS tuning works well on the G3, and makes some weak, beady sounding stations much steadier and stronger.
On mw, the set is sensitive (similar to the G5) below about 1100 KHz down into the lw band. With sync or ECSS tuning, stations emerge from nothingness near the upper part of the am range, but is still less sensitive than the G5. Overall, the performance ECSSwise and sync make the G3 a satisfying set.

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