Chris,
If I were in a situation where a #12 is not dark enough, I would seriously consider wearing some wrap-around dark glasses under the hood to help block internal reflections. I've always found this to be better for parched eyes than just going darker in the hood. Another trick when using conventional filers is to wrap the lenses and cover plates to gether with black electrical tape to prevent leaks around the edges of the lens frame. These light leaks not only come from poor fit of the frame But, the plastic coverplates transmit light to the edges and cause internal glare within the lens assembly.