Lets see if I can "paint" a picture of the process.
When the painter applied a nice coat of paint to the fender lip, from the rocker panel at the front of the wheel well up over the top and down the back edge to the pinch weld of the quarter panel to the trunk floor, 90% or more of the paint went to other surfaces other than that thin fender lip. Allot went onto the sound deadener directly above, behind that fender lip but often produced a shadow (thin with a very soft edge) directly behind the lip. On the top 3rd of the wheel well the inner panel is angles such that the overspray shadow was increased due to that angle.
Next as the painter applied paint to the quarter panel - passing the flowing paint gun over the wheel well opening (flowing all the time) a great amount (100% of the paint coming from the gun) passed into that opening directly on the inner surface of the wheel well and frame rail below it. In addition the large amount of overspray settled on the bottom of the floor in that rear end tunnel and surfaces near by
To illustrate this I offer the following pictures. Pictures can often be difficult to find since many owners blacked out the wheel wells over the years or cleaned them - strippign away the top surface from the somewhat soft sound deadener (at least somewhat flexible) removing the top paint
Hope this helps