As I recall, you are in Korea and are using flours from the U.S. and Canada. If the protein content of the flour you are using is 13% (on a dry weight basis), and are using the Honeyville vital wheat gluten (http://shop.honeyville.com/vital-wheat-gluten.html
), which has a protein content of around 75%, then, according to the Mixed Mass Percentage Calculator at http://foodsim.toastguard.com/
, the protein content of a blend of 965g of flour and 35 grams of the Honeyville VWG, for a total of 1000g, comes to a bit over 17%. That is far too high. A protein content of around 14%, which is typical for a high-gluten flour, would be satisfied by a blend of about 984g of your flour and about 16g of the Honeyville VWG.
Different flours, even those with identical protein contents, can have different degrees of gluten formation. That is because gluten can vary both in quantity and quality from one flour of a specific type to another of the same type.
In general, the higher the protein content of a flour, and all else being equal, the more water it can absorb. Factors that can affect hydration of a given flour include the age and storage conditions of the flour, its moisture content at the time of use, any crop related damage (including starch damage), any damage during milling of the wheat grains, any insect infestation, and long term effects of humidity. Ingredients that are also added to the dough, such as oil and other wet ingredients, and also dry ingredients, can also affect the hydration of the flour.