The tempo downbeat or subdivision settings shouldn't affect the MIDI beat clock. The way that works is that on every beat, it queues 24 MIDI messages for the external device, with equally spaced timestamps. Then the iOS MIDI framework sends the messages, and the external device measures their interval and calculates a tempo from that. I would like to know if Set List Maker's own tempo clicks feel accurate on this device, and that would tell us whether Set List Maker, or the iOS MIDI framework, is what can't keep up.