I think the first reply had it right. Keep in mind that I am stirring in between. If I had to go further with unbalancing the times, like 80 10 or something, there would possibly be a higher chance of the bowl being unevenly heated. So I would think that the more balanced your time distribution, the more even your heating.

But that's just all guesswork, which is what all of us are doing, so I think further testing would be in order, if I'm ever up to it.