Microwaving food: longer on lower, or shorter on higher?

Factual Questions
1

Of course, we all know by now that the so-called “power settings” in a microwave oven simply mean that on “high,” full power is applied all the time, on “medium,” full power is applied half the time and so on–it’s not like the microwave energy is “less” on medium than on full.

But I’ve noticed differences while reheating, say, a bowl of spaghetti, in whether I do it for a shorter time on high, or a correspondingly longer time on medium.

In the first, high-power case, (note that I always cover the bowl with cling-wrap to keep moisture in) sometimes the individual strands of pasta shrink and become tough and chewy.

Of course, if you do it long enough, this will happen on medium, too, but I find I generally get better results on all foods with longer reheat times on lower power settings.

Any ideas why this should be the case, other than a simple matter of heat having more time to distribute itself in the food?

2

Hot spots develop in food that is heated in a microwave because the microwave field strength varies from point to point in the oven.
The rate at which food heats in a microwave increases with increasing temperature.
The combination of these two factors sets up a positive feedback cycle which can result in some parts of the food getting overly hot while other bits remain cool. Pulsing the power minimizes the feedback.
This link [Pulsed microwave heating of agar gel](Pulsed microwave heating of agar gel), supplies a bit of data on the effect.

3

Having the microwave cycle will allow any hot spots (in the food) to even out as the heat from that spot conducts (moves) to the surronding area.