Hydration adjustment with different flours

Let's say you make a free form artisan loaf with all purpose flour and your hydration is 85%.   The next time you bake you use bread flour.  Now if you use the same amount of flour (the same hydration ) you will have a stiffer, drier dough.  So how do you adjust for the greater capacity of bread flour to absorb water?  Is there a factor --  1.1x or 1.2x or whatever?  Or is it just trial and error?.   Certainlly, going by just the "feel" of the dough is chancy.