This is an old trick that often works. Make yourself look unaware and climb a bit at an angle, when you see the enemy pointing their nose up, launch in off bore. Then go back to the notch, and be careful of AIM-9M if applicable, preflare.
You are baiting into getting shot, but that’s fine because you can fire back and go back to your notch very quickly.
Here is an example at very short ranges, but you can still do it with aim-120, just not at such an aggressive angle.
A good player would launch without pointing the nose up and possibly approach you at an angle to match your notch, but sometimes people just assume you are unaware and make mistakes.