You will start the decreases at the same 5 inch mark, but to shape the hat the same way at the top you will have to change the speed with which you decrease. Say if the top of the hat is shaped over a distance of 2 inches with the yarn that gives 16 st=4inches, yarn that is 24 sts=4 inches when worked the exact same way would not make as long a top because the stitches are not as long. I would bascially decrease it the same way, but play it by ear about when to decrease. You might, for instance find that 2 rows of even knitting between the decreases (most hats give 1) will work. You don't have to have everything the same all the time. I mean you don't have to have the same number of rows between decreases each time, it can vary. Try something and see what result you get and if it didn't make a satisfactory top, rip that part out and try again.