I post these pictures in an attempt to show what the target opening looks like from both front and rear. This opening on this small deer was 1 3/4 inch across. I am only guessing that it would be about 2 1/2 inches on a large adult deer. As you can see. The sternum at the bottom is a large bony mass that if hit with an arrow will not offer much penetration but plenty of opportunity for deflection.
On either side of the opening the ribs (viewed from the front) make a solid wall of bones that are curved and are at a glancing angle. If you did go through the ribs on either side of this small opening, you would hit only one lung. If you miss the opening and shoot high, you do have a chance to hit the spine if you shot does not hit right or left. The spine is a cord that is smaller than an index finger as you can see in the pics. While it possible to make this shot and bring a deer down it does require the highest degree of accuracy to ensure a quick kill. Again. Take from these pics what you will. This is what your target area looks like
From the front. Neck high, sternum low and rib on both sides
From the inside looking out.
The spinal cord in the neck, near the frontal opening. It is very small and well guarded by heavy bone.
A cross section view. The cord is enclosed in solid bone.
I do not mean to tell you how to hunt or tell you which shot angles to take. I post this only to let you know what the frontal archery shot looks like beneath the hair.