Bottling carbonated Beer (finding the right pressure)

I have Blickmanns beer gun the "Last Straw" and have built a forced quick carbonator to speed up the cabonation process and then bottle my beer. My issue is that I follow the PSI levels for the beer style I am carbonating and it turns out great. My issue is when I bottle it from there it turns out Super Flat. I have a English Pale Ale and I pressured it to 2.5 or 10 PSI at 35 degrees for that style plus I added 2 PSI per Blickmann guide. If I draw a glass of Beer from the straw it is Great. But if I bottle it at that same pressure and and open it the Beer is Flat. I presume that I need to increase the pressure but is there a guide to make it right.