Suzie, didn't you say that you have previously tended to ride with your weight on the nose of your saddle? Is it possible that you are still trying to break this habit?
I would think if you are feeling a need to scoot back in the saddle then it's one of two things: a)the saddle nose is a bit too low, or b)you need to push your saddle BACK 1/4 to 1/2 inch (back as in towards the back of your bike).

I think this saddle is going to be just right for you once you get the fine tuning down. It took me a couple months to get to know the exact optimal position for my saddle. You're a fast, lightweight and long-boned rider who is going to be doing long distances...a good Brooks candidate if I ever saw one!

By the way, my "Spring season sitbone soreness" is totally gone now.