there are a couple ways to tackle this.

1. Add your hair in stages. Start your thread and put down your glue and use a minimal amount of hair on the first wrap. Sinch it down and add hair. Rinse repeat till you have the right amount of hair and the build up you want. This is the most common way i use to build up. (BONUS) If you can get it to where you can do it in two steps of adding hair you almost create the visual of a fish tail.

2. Use flymaster 6/0 its a little thicker than 3/0 and takes less to get the build up.

3. Go to the end of the calf tail. Down at the end the hairs are a tad thicker and little corser of hair. They also for some reason have an aura of translusence(sp).

There are many ways to do this. I have so many how to videos to make i need to go and buy my own camcorder.