Back to front: 196 instructions
Front to back: 195 instructions
And I tried normalizing against the min and the max. It helps, but it is still some ways offset. I am going to try to see if I can use the depth buffer to limit the steps more directly. If SceneDepth < CamToEntry + CurPosInsideVol then it has gone too far. I will have to try things. Maybe I have to manually send in the bound as a uniform to the shader. But this is just things I have to test.
If I take the first step before the loop I end up with the circular artifacts turning black: 
I have a timeline on my volume, but I am simply doing that by making several textures for the volume over time. I did not need to blend between them, but I am thinking about adding another texture I look up and blend between their timeframes.