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A sub directory is never going to rank like the home page. you can look at linking to try and improve the rank http://thatsit.com.au/seo/tutorials/a-simple-explanation-of-pagerank I would try and push PR from all shop pages to the shop main page, not the root. Myself I would create a sub domain shop.bouldersuk.com, you will stil be seen as the same site, but will be easier to have the main shop page seen as a home page

the mozbot updates about every 2 weeks, but the data its based on is from a few weeks before that (over a few weeks) So best case it will be 4 weeks before the mozbot will show your changes to your PA/DA, but more likely 6-8 weeks