This is somewhat connected to a previous thread about WTIC 1080 IBOC blocking 1070 but not 1090.
I tried an analog tube tuner which has a 'Whistle Filter' which if you are not old enough to remember those, it is a sharp filter 10 Kc. above and below your tuned AM frequency to cut interferance. That did not work, but I did hear a promo on KYW 1060 AM that THEY are HD, which I think means IBOC from both above 1060 and below 1080 on 1070 which may be why 1090 WBAL is not effected by IBOC from WTIC.
Not sure how precise a ICOM R-75 is in tuning read out, but here are the freq range I hear the three stations on.-
I don't have the radio theory knowledge to draw conclusions, but maybe some one else here does. It's just an idea and some little tests. - FARMERIK