What is the transparency lock's maximum percentage?

I'm trying to color over transparency with a locked alpha channel to see what things will look like before applying it to the fully opaque layers. The problem is I can't use the eraser tool to reduce opacity with the alpha channel locked, and after I unlock it and erase the color to 1% opacity, it gets locked with the alpha channel and I can't do anything with it.

What is the maximum percentage of transparency that the alpha channel lock will affect? I want the pixels to be as transparent as possible without being affected by the alpha channel lock so I can stay within the area I want to experiment with.

Edit: I know I can use selections and such, but for what I'm doing I need the "selection" free because there's pieces within that area that need to be colored separately, which I can only do by selecting them or creating more layers.