Just wanted to remark, you can have two solenoids tied into a single zone, which would make that zone open both. That’d be a minimum of 10 “shared” zones, which would leave 6 standalone zones on a 16-zone controller.
By doubling I’d expect to see a drop in water pressure/flow to adjust for. In terms of this particular feature, I’d expect a doubling of baseline current draw. It would then only be able to tell you about deviations from that baseline for the pair of valves tied to that zone.