Perfect Cookies

I recently started to read a book on the search for the perfect chocolate chip cookie. I saw two suggestions that were interesting: (1) if you want to have a cooked, but soft, cookie, substitute about 2 Tb. of corn syrup for 2 Tb. of the sugar; (2) you can reduce the amount of shortening by 1/5. I tried this in a chocolate chip cookie and didn't notice too much of a change, probably because I used a recipe that included oat flour and that always does different things to cookies. Then I tried it with a standard peanut butter cookie. For the 1 cup of fat, I used 1/2 cup butter and 1/3 cup shortening. I substituted the corn syrup for part of the white sugar. I baked the cookies for 11 minutes and could have gone a bit longer. Now, even a day later, the cookies are still crisp around the edges and soft inside. These cookies always went hard on me by the time they cooled. If you try these techniques, what happens to your cookies? Is is different close to sea level versus a high altitude?