Ha-ha, yeah I respond to bunches of stuff. Like a cat, ready to pounce on the unsuspecting and help them with their home improvements and repairs.
90% of the time when I get oil canning with aluminum trim, it's temperature related. The expansion rate of that thin aluminum in the sunlight is much greater than the wood behind it.
Have you ever tried using a break buddy? It uses two rubber tires called dies to form a reinforcing rib down the length of your trim. It doesn't eliminate oil canning, but it breaks it up and makes it less obvious. It makes a bigger rib than you see on store bought fascia.
I worked for a company that wanted the nails driven upwards through the bottom. You can't get many nails in this way. There were many warranty calls for trim that had blown off. I could still see some oil can wrinkles when it was nailed from the bottom. It just followed the bend and twist of the lumber, maybe worse than face nailing.
All of that said, what works best for me is, a slot cutting punch used along the top edge. Push the drip edge up and nail the top through the slots loosely. Then a nail every 2ft up through the bottom. The slots will show with narrow drip edge, so it may not work on all jobs.
You sided this house in December, betcha' it's the temperature causing expansion. Oil canning wrinkles are a fact of life. It happens to the best siding guys. If the customer forces you to replace the trim, lay it in the sun for a moment before you install it. Use less nails (as high as you can get them and then down on the bottom). If the house has gutters, at least you won't have to replace that trim!
Sorry Bob, I know this doesn't help you much, but settling usually doesn't affect the rake boards on the gable ends.