How to determine "The max step size" in SIMULINK in order to obtain right simulation results?

This question came about when I was trying to build a very simple circuit, "op-amp circuit", which is also an example in SIMULINK as the pic showed below.

I created a blank model and copied the example circuit in it. Then I ran the example model and the copy model and I noticed the waveforms were different! I thoroughly compared the configuration parameters between the example model and the copy one, and finally found that "max step size" caused the problem. The example model set it to "0.00002s" while the copy one to "auto". I tried to increase it to a larger number, and the waveform of the example model became wired as the copy one. So how should I know if the step size is small enough for getting correct results?