So on the fenders and valences, I'd do right to give the back sides a full coat of red oxide with only slight over spray of gray that I assume was only directed towards the exterior surfaces?
You have appear to have the general idea of what took place. I've found it difficult to describe and demonstrate how these area turned out since most of even the nicest cars were not well maintained in that area, often got covered with undercoating and sometimes sound deadener. Any cleaning removes the lighter overspray and your looking for something in a typical range rather than an exact amount of paint and or overspray.
In an attempt to show to the members I offer the following
This is an example of a fender that got allot of exterior color applied indirectly and directly to the back side.
The blue areas would have been the direction of application to make sure edges and visible surfaces got a nice coat. The green arrows would have been the pockets or shadows hidden from most of the paint. Difficult to see in an example where the exterior color and the red oxide isn't greatly different
The other end - same arrow indications
Back side of the valance with the shadows produced when painting this car/ Red arrows indicate where there is likely an unseen shadow from the lip that can't be seen from this angle
Later example showing a light but fairly consistent coat on the back side
Later car but this (though cleaned off allot) shows the affect of the painter painting the fender lip and in turn the paint was applied to the top of the headlight bucket area.
And my final example. This is the same car from two different sides. One the first very little overspray made its way to the back side of the headlight bucket area
While on the back side of this fender you can see the misty affect of the Ivy Gold application creating a chalkier final look to the same surface