It sounds to me like your comfort zone shots are right on, but the pressure cooker shots could use a little work. The situation could mentally be tearing down your shot, I don't see it as physical or being a lack of practice. It is very difficult to replicate this mental situation in practice that will actually help. You maybe able to do some visualizations (it takes work) that will raise your heart rate and hopefully come close to duplicating the real thing. Maybe try taking your unsuccessful shots (something that you already had an experience with) and replicating the emotional feeling starting at the time you first saw the game, the only difference is to visualize yourself with perfect form and having the shot hitting the mark. After perfecting this, then maybe take it to a 3d target with your bow. Visualization takes practice though and there are a few ways to do it. First is to see yourself as if you were on TV (this is a bit easier), second is visualize and actually feel emotional and physical characteristics (second way is a bit better) during the visualization.
Disclaimer: It is not for everyone. But if it helps, great.
Below is a quote that I kind of like:
This is kind of neat and is as applicable to today as it was in 300 BC:
"When an archer is shooting for nothing he has all his skill.
If he shoots for a brass buckle he is already nervous.
If he shoots for a prize of gold
he goes blind or sees two targets
- he is out of his mind!
His skill has not changed. But the prize
divides him. He cares.
He thinks more of winning than of shooting
and the need to win
drains him of power. "
Chuang Tzu