Oh, the irony of the thread title 'Everything You Need To Know About Topical Dutasteride'.
No one has a clue. Apart from a few anecdotal cases, the results are non-existent/unsubstantiated. To fill the gaping void in empirical data, we have all the marketing B.S. about 'vehicles' and % of active ingredients. These companies are selling a product and need you to buy into their storyline/USP. Don't get suckered in and lose sight of the real reason you use a product, RESULTS.
Start with the results (if you can find any) and work back. Only if there is a pattern of success, you may indulge in theories on why it works. Everything else is just hot air filling up bandwidth.