Heat resulting from voltage drop?

If having company makes you feel any better, my setup is just the same with a straight plug in the cabinet. The power to my microwave is probably pretty typical: 25 foot shore cord, romex to the breaker box, romex to the slideout area, connector transition to flexible cable, transition connector back to romex in the slide, another connector where the romex comes out of the slideout wall, finally romex to the outlet the microwave is plugged into. Sometimes I'm surprised the darn thing works at all! It's all 12 gauge. I'd feel a bit uneasy using even a 14 gauge run. You could always cut the plug off the existing cord and replace it with an angle plug. They're not as slim as the one in your picture, but a lot better than the straight plug.