For frequency shift islanding detection method (simply referred to as frequency shift method), a very common active method, it is pointed out that if only parts of inverters employ this method, their disturbance strength may be unable to cause the frequency to exceed the limit. And then two related issues are raised: the rate of the inverters employing frequency shift method and the adjustment of positive feedback gain of frequency shift method. For the rate of the inverters employing frequency shift method, in the most unfavorable case, a relationship between it and the maximum overload factor of an inverter is achieved. The relationship shows that this rate can be smaller if the overload capability of inverters are larger. For the adjustment of positive feedback gain of frequency shift method, a relationship between it and the rate of the inverters employing frequency shift method is obtained. This relationship shows that the positive feedback gain should increase according to the rate of the inverters employing frequency shift method. Simulations are performed and verify the previous conclusions.