I'm rather impressed that you placed at all posting the jog. Most judges either dismiss, don't place you, or put you last of the ribbons if the class and show are that small. I swapped to English to show because my horse at the time had a heinously rough trot, neigh impossible to sit, let alone look good doing it.
It's ok to post western to any variation of the trot schooling, trail riding, etc. (a true jog is much easier to get sitting; the rider's much more able to influence the gait from their seat sitting), but in any competition setting, no posting in a western saddle.