The correct contemplative practice (vipaśyanā-caryā) should be done like this

Four Foundations of Mindfulness Contemplative Practice (vipaśyanā-caryā) Diary: Currently I enter shallow samādhi fairly quickly. During sitting, I raise a "knowing," and along with the breath, keep illuminating it within the mind, illuminating and illuminating... Before long, with a click, the mind seems to enter the stream, instantly pure, and the brain becomes pure and bright as well. 

There is no need to deliberately deal with wandering thoughts. The physical body, feelings, and wandering thoughts are all arising-and-ceasing illusions, empty; they are not bondage. Just keep illuminating them, no need to counteract them—they become empty on their own. As the Heart Sutra says: “观自在菩萨，行深般若波罗蜜多时，照见五蕴皆空，度一切苦厄。舍利子，色不异空，空不异色，色即是空，空即是色，受想行识，亦复如是。” In the past I only knew how to recite it, not how to apply it. Now, in training, when I put it to use, I seem to have found a bit of the feel for it. The five aggregates (pañcaskandha) are not an obstacle and need not be dealt with; one only needs to remember that they are arising-and-ceasing illusions. Just keep illuminating them and let them be. After illuminating them for a long time, the five aggregates will become empty by themselves; the physical body and wandering thoughts will automatically become empty. This is what I can currently know. 

Sitting cross-legged is merely a form. I have also tried sitting on a chair or lying on a bed, raising a "knowing," illuminating within the mind, and proceeding this way—I can also enter relatively shallow samādhi. When sitting, full lotus, half lotus, or loose cross-legged are all fine. The key is the method of applying the mind; if the method is right, one can enter. 

Assessment: When the mind is not calm, there are many objects of attention within, but we have a goal—contemplative practice on the breath is the primary goal, one might even say the only task. Grasp the main matter, grasp the great matter, and only then can the task be completed with quality and quantity assured. Do not chase after thoughts beyond the breath; those are unimportant. Thoughts come and go and never stay; even if you tried to keep them, they could not be kept. Just do the proper work without distraction. 

When the mind rests only on the breath, like a lamp shining only on the breath, all the bodily sensations and stray thoughts around it are no longer in the mind—they disappear, become empty. And on the breath, one will discover phenomena that could not be discovered before, that is, the truth, the facts. As for what those truths and facts are, each person experiences them for themselves in the course of practice; what each person discovers may differ somewhat, but the final result is the same by different routes: realizing the emptiness of the five aggregates and no-self.

In contemplative practice, the specific posture does not matter; one must practice whether walking, standing, sitting, or lying down, combining movement and stillness so that they complement each other. But sitting cross-legged has its advantages: it can promote smoother circulation of qi and blood, make the physical body more harmonized, the mind calmer, and thought more concentrated. Afterwards, combining it with walking activity, the circulation of qi and blood receives full regulation and pervades the whole body, which is more beneficial to the body, and the mind will be more pure.