Thank you, IsaoShi. You are of great help to me.

Here is a "test" shot of the interior of my Blockhouse again, now using the correct version or one of the corrected versions of bagginbill's ISF shader.

It has only one light source simply to test the effects of the shader and to just see what's what.

The setting for this ISF light are as follows:
Dist Start 0.000, Dist End 0.000, Shadow 1.000, Intensity 100%, Shadow Blur Radius 0.5, Shadow Min Bias 0.8, Atmosphere Strength 0.01, and in the ISF shader the Intensity_Distance Value_1 is set at 60 inches. I did not change any other settings.

For what it's worth, I think this test is doing what's suppose to do, figuring out things.
If I keep the Intensity_Distance Value_1 low enough, I eliminate the need for a second point of light within the lantern to emulate a bright flame. I did run a test with a Intensity_Distance Value_1 set at 120 inches, but the light seemed to bright within the lantern.

And that is where things are at the moment.