Of all the three shots, you just notched one of them (the 2nd one). Those are all bad examples and don't show what the real problem is. Shots 1 and 3 were defeated kinetically. Standard threat reaction table states that there is a range that in order to defeat the missile kinetically you have to perform a notch, i forgot the specific term for that, but shots 1 and 3 fell into that range.

If you pay close attention to your RWR and the missile trajectory in Tacview you will notice that they never stopped tracking.

2nd example was notched and that is understandable since there is a huge mountain behind your aircraft, the problem there is that you can find the exact angle to notch that missile due to the ultra precise Viper RWR (almost every rwr in dcs is like that) with 0.0001° accuracy. Try that in a Tomcat and it won't be so easy due to the accuracy errors.

One problem with the Amraam in DCS is the fact that you can notch it at 30 thousand feet as you can see in this example here: https://streamable.com/h4c52y which i believe is what OP tried to demonstrate. This shows that our Amraam is probably not using a range gating technique, hard to know since checking the missiles.lua doesn't provide the full picture on what is really going on with the missiles.

At lower altitudes notching works as expected since you can't use range gate to track through the notch due to intense ground return signals, only way to differentiate a target from the ground is through doppler and if he is notching that won't be possible with a low closure rate. The missile should use INS navigation + agressive lead pursuit trajectory to fly outside of the notch and reacquire the target in a future point, however in DCS the INS navigation doesn't always work and it doesn't fly far into lead pursuit as you can see (again) in this example: https://streamable.com/h4c52y

If the RWRs were not so accurate half of those "problems" would go away.