The texture and yield is governed two factors: developing the gluten completely and washing out the bran and starch effectively.
To develop the gluten, combine the flour and water into a workable dough and give it 50 light strokes. Cover the bowl and let it rest 10-15 minutes. It is during this time that water chemically combines with the flour and the strands of gluten form. After resting, return to the dough and you will notice it has a different feel. It is because the gluten has formed. Knead the dough 100 times. Immerse the finished dough in ice water or at least very cold water for at least 30 minutes. An hour is better.
To effectively wash out the bran and starch it is essential to work the dough under alternating hot (as hot as your hands can take) and cold water baths with 30 minute rest intervals each time you change the water. Start with hot, work the dough with a spreading motion for a few minutes. Pour the water into a bucket (not down the sink!), cover with very cold water and let it rest 30 minutes. Repeat and cover with hot water. Let it rest 30 minutes each time. Usually during the third round the dough will very soft and your hand technique should become one of gathering instead of spreading. If it feels like you are on your way to pancake batter, pour it through a fine colander to gather the gluten and give it a cold water bath. In the last couple rounds it will become increasingly firm and the strands of gluten are evident.
Finally you have a ball about 1/3 the size of the original dough. I divide this into baseball sized pieces and drop them into a boiling pot. Return to boil and cook until the pieces float to the surface. Remove and put in cold water. The shape of the pieces is now set but they aren't yet fully cooked. From here cook in a broth seasoned to your liking. I simmer them for 2 hours in a simple kombu, tamari and water broth.
I use fine ground whole wheat flour. Stone ground will work but yields are lower and texture is inferior. My dough formula is 2600 gr fine whole wheat flour and 1900 gr cold water which produces 2000 gr finished seitan. Hope this is helpful!