Yes you do in Jackson, MS.
Maybe so, but one church in Jackson, MS hardly qualifies as the Antiochian Orthodox Church in America.
I can't say much regarding the Diocese of Miami and the Southeast, but in the Diocese of Wichita and Mid-America, kneeling on Sundays is prohibited for the exact reason you stated earlier. I would think that this practice is the norm elsewhere and that what you observed in Jackson was an exception, but I'm just guessing.