I have a Bosch pressure washer and I put the Kärcher cleaner in a special container, it cleans well and was enough for my 30m2 terrace - I don't know exactly how much the Kärcher pressure washer sucks in, but I think it is probably very similar, and another important factor is how fast you move the device back and forth when spraying.
The instructions for use state that the agent should first be sprayed and then after about 10 minutes of soaking, the high-pressure cleaning should be started.