I don't know the exact temp of my iron but if the instructions say to use Medium heat or Cotton Setting or Polyester setting or High setting etc, then I'd make sure I did that. And they should say how long to hold the iron to it, and whether to use a press cloth (some want wet and some want dry). So following that brand's instructions are important.
For instance, I use Heat & Bond Lite often and have found that if you heat it too much, the glue will melt through to the other (front) side of the fabric you are fusing to, leaving a little shadowing. So I am careful not to exceed the time recommended, which if I remember correctly is about 8-10 seconds. Conversely, if you don't heat the glue long enough, you can see that it's still opaque and not clear, so then I give it a tad more. And if you way over do it, it can have a poor bond. But in general, I think whatever the name of the setting on your iron that corresponds to the instructions would be fine.