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So, keep in mind that "cheating" Page Authority isn't really very useful - we're just creating a predictive metric. We have no control over whether you actually rank. PA is a machine-learning model designed to predict the ranking ability of a page, but it's far from complete or perfect (no one number can be, although we're trying to improve it all the time). Sub-domains are tricky animals. Sometimes, they inherit a lot of power from the root domain. Sometimes, they get fragmented and essentially act like entirely separate domains. Our PA model doesn't really account for all of that complexity. It's a best guess, ultimately. There are certainly cases, though, where a sub-domain ranks well without many unique links, solely based on the power of the root domain. That's far from guaranteed, though.

Yeah htaccess is the right way to go about 301 redirects.