Greetings everyone, and thanks for the ideas on improving my pain au levain and pate fermente crusts. The interim answer seems to be summed up in one word.."MORE."
More heat. Notwithstanding the global warming debate which ignited in my last post, getting my oven hotter - sooner appeared to help, and improved oven spring.
More heat, longer. I now do not immediately turn down the temp from 500 to 450 after initial entry.