At this point I am not convinced it is one particular place over another. Comparing the bleed down times is a great idea, I'll get back to you on the results. About all I have to go on is that it only shows when the engine is in reverse for an extended period of time then the a normal full stop landing. Once the prop comes out of beta and normal airflow through the nacelle resumes, the light extinguishes.
I am away from home station and have little resources to fabricate a plug to be able to pressurize all the nacelle ducting independently from the rest of the bleed sys with some shop air. I am going to head back out to the plane to troubleshoot some more and let you know what I find.