do you have a stud gun? i use one to shrink when needed, very handy tool. to me that area under your ruler needs to be shrunk some, if its oil canning there. what makes it oil can is the metal has moved to that area and has no place to go (under tension) so it pops in or out. i would shrink it some with a stud gun and bump it out, rubber hammer maybe. remember every time you hit the metal with a solid hammer it stretches. also to much shrinking can cause the same thing or cause that whole panel to suck in. i would run a long flexible straight edge along the trim holes from the door opening back as far as you can to check. flexible straight edge, i use several different lengths of 3/4 wide steel banding material.
Jay D.

The hood on this Jeep Project is a great of example of what happens when people try to put filler over an area that is oil canning.

You will also see my first attempt at using a stud gun to remove the oil canning.

viewtopic.php?f=12&t=23656&start=40
Go to page 5 to see the hood.

A stud gun with a shrinking tip works good to localize your shrinking.
Jay D.