How to detect properly when the player can crush an enemy from above? - unity3d

Question

This question is much more complex than it seems, here's why.
I have a player and the physic is enabled, in a 2D + 3D world.
The monsters have a sinusoidal movement = they go up and down, from right to left.
The player can only jump more or less high, but can't move right or left (like the dino game on Chrome when there's no Internet connexion).
After many unsuccessful attempts to detect if the player is above (it's not simply if (PlayerY - MonsterY) > 0 otherwise I wouldn't ask here), the best idea I came up with is to make two colliders in the monster: one for the "head", and one for the "body".
When the player hits only the head it can only be above (otherwise it's the body first), so it's an easy situation
When the player hits only the body it can only be below or on the sides, so it's an easy situation too
sometimes, it happens that the player hits both colliders.
So I'd like to check this after the FixedUpdate calculations.
If you read the execution order of the callback functions, there's no LateFixedUpdate: even though there's a LateUpdate, it's officially written that the developer should handle physics in FixedUpdate, and nowhere else.
What I've done so far is: when the OnCollision of monster head is called, just change a boolean, and same for OnCollision of the monster body. So after the OnCollisionXXX, like the documentation says, there's only one thing you can use: yield WaitForFixedUpdate.
I'd like to check those booleans and act according to their values in the yield WaitForFixedUpdate.
I can't find any valuable example on the net on how to do this. Any idea how to implement yield WaitForFixedUpdate in this situation? I'm stuck.

Answer 1

To the question
how to implement yield WaitForFixedUpdate
The yield is ment to be used inside of a Coroutine
yield kind of reads like "interupt the routine here, render the current frame and continue from here in the next frame."
e.g.
private void Start()
{
// Start the routine once
StartCoroutine(LateFixedUpdate());
}
private IEnumerator LateFixedUpdate()
{
// looks scary but is okey in a Coroutine
// as long as you yield somewhere inside of the loop
while(true)
{
// Continue after all FixedUpdate has been called on all scripts
yield return new WaitForFixedUpdate();
// do something
}
}