However, if this is a small town, perhaps the people who run the PTA all know each other very well and have many overlapping interests. Other parents from outside may not understand how decisions are actually being made. So the PTA is still low context, but it has a high context subgroup that is in turn part of a high context small town society. If culture encompasses a number of perspectives and strategies, some will be routinely available. Some are not commonly used, but no one objects if you do.
Individuals choose based on their personalities and situations.
As cultural groups intersect, they may start to borrow options from each other. Over time, people's general choices will shift, although the culture will still offer up a limited universe of choices, those set of options changes.