You don't change your draw length. Your draw length is your draw length. A loop only adds about 3/8ths of an inch to your anchor position. Your string should still contact your face in the same place as it did before.

The only differance is your anchor point will be slightly higher due to you moving your release from below the nock to behind the nock and slightly farther back due to the length of the loop.

When you change the location of your release your anchor point changes in direct relation to these changes.