One of the biggest choke points on the 9000 sensor is the unions. The inside diameter of the 9000 sensor is 25mm. The unions are 19.75mm ID on the imperial unions. Anytime you restrict flow or narrow it like that, it reduces flow dramatically.

In a perfect world the 9000 flow sensor would have larger unions that can accept 32mm or 1” pipe. Flow would be much better and you would be able to achieve greater flow.