it might make sense to make the default maxSetSize to be something that depends on hllBits. At the extreme you could serialize every item coming in and increment a byte counter (although the in-memory may be much less or more, but still), then when it exceeds 2^hllBits, switch over. I would think something like maxSetSize: Int = math.max(10, 1 << (hllBits - 5)) might be a decent default.