No problem, they did as they were intended, provoke a buff for the longbow. Also I quite enjoyed doing something with those calculations, it made me feel happy to know I had done something to influence the devs all with the use of some easy mathematics. Thanks goes to Paul mainly, since he took my calculations in to account then checked them with the hard coded ones, hes the one who got this changed and showed me the real equations. So i will use them in the future. As for automating them, one of the pages Paul linked me had some pseudocode on there already, so I can link that here if Paul is ok with that and you want it.
I also just remembered reading that PD has the most effect on accuracy in the first 2 levels above your bow difficulty, which seems very true. Thats why for the next build I am going 24/15, which will give 147 archery WPF and 8 PD. Just for anyone thinking of an archer build but isn't sure.