If the reproduction rate is 10, and you catch 70% of cases, then the effective reproduction rate will be closer to 3. Since even the highest estimates of the basic reproduction number are only about 4, a test that's 75% accurate means an effective reproduction rate closer to 1.
Are you aware of the difference between 4^x and 1^x?
Are you aware of the difference between 4^x and 1^x?