You probably don't have much margin for error.
If the flow drops even a little bit due to a dirty filter or clogged baskets, the heater will turn off.
You have to give yourself some margin for flow drop depending on how much the flow will drop in normal conditions.
If you are really good about keeping the filter and baskets clean, you don't need as much margin.
You want to avoid the pressure switch being right on the edge of closing or opening, which will cause operational problems.
If the flow drops even a little bit due to a dirty filter or clogged baskets, the heater will turn off.
You have to give yourself some margin for flow drop depending on how much the flow will drop in normal conditions.
If you are really good about keeping the filter and baskets clean, you don't need as much margin.
You want to avoid the pressure switch being right on the edge of closing or opening, which will cause operational problems.