What is a good anchor and why does it matter?
As in all things archery, consistency makes for accurate shooting. A solid, ‘tight’ anchor allows and enables many positive things. You and your coach should explore what is right for you.
A tight anchor should have as much contact as is practical between the index finger and jaw line.
A proper anchor should allow for a clean release, with no string to face scraping.
An anchor should facilitate better body lines.
A good anchor should enable you to engage your back muscles easily.
Whew, that sure is quite a bit to expect from one not so simple position in your shot. I often see very weak anchors, which lead to inconsistent shooting. You and your coach should explore what anchor is best for your body type and shot. The payoff will be more consistent shooting and tighter groups.