There is a big difference between yielding for pressure and evading pressure (physical/driving pressure). Even if it does seem the same at first. When you ask your horse to yield for physical pressure, let’s say on the hind quarters, and the horse moves already, before you even made physical contact, then the horse is not yielding, but evading the pressure. You then only ask 1 step and you get 10 at once.
Also when you ask to yield for driving aids (indirect pressure), this can happen. Then, for example, you ask your to yield for driving aids with the hind quarters, and the horse does it way too fast, in a tense and insecure way.
How to notice the difference between yielding and evading?
If a horse evades the pressure, you can see this in the fact that it reacts too early, too fast, or too long. The horse moves away further than you asked for. The reason is often because you put too much pressure in the learning phase or you still do too much: you use too much pressure without you knowing, like too big and/or fast movements and your energy and bodylanguage is dominant. If that is the case, you could even say that your horse is reacting in an equal way on that, and that the horse is not really evading, it's just reacting in the appropriate way on the pressure you put and that is too much pressure.
If a horse really yields, it stays calm and relaxed. You can influence how long the horse yields (so you can also stop it from yielding) and you also have influence on the speed: you can let the horse do the exercise slowly or faster, without the horse rushing in the exercise. A clear communication can be felt and is visible in the exercise.
So to prevent the horse from evading, you should also be calm and relaxed. You act friendly but you’re also being clear. A lot of touching exercises in-between are good, especially when your horse has become distrustful by a wrong approach or a bad experience or when your horse is super sensitive.