What level of attention I should pay on the meditation object?
There’re two scenarios during my meditations. 1) I pay gentle attention on the mediation object. Thoughts arise from time to time. My attention splits between the thought and the object. I bring back my attention on the object.
2) I pay strong attention on the meditation object. This requires more effort. Almost no side thoughts appear as my attention is 100% on the object. But I feel I cannot go deep.
How to achieve absorption?
In meditation we try to be 100% focused on the object of our attention.
However, absorption comes from a combination of two qualities: on one side there needs to be complete focus, which means high energy and inner intensity. On the other side there needs to be relaxation, calmness, receptivity. These two sides, you might say, are our masculine & feminine meditative qualities, which need to "marry" to bear "the child" of absorption.
If one of these two qualities is missing, inner absorption cannot happen. Your point 1) above seems to relate to being more relaxed, while your point 2) seems to refer to the high energy side.
I don’t know your specific case, but usually everyone needs to develop and strengthen one of these two qualities. For example, Swami Kriyananda has always been an extremely high-energy person, so Yogananda told him to give more emphasis to relaxation in his meditations. To others the Master talked about "intensity" and "prolonged intensity."
Yogananda himself exemplified that combination of qualities: he manifested powerful and focused energy, but also said (he was sitting at a desk): "As I sit, the lower part of my body is so relaxed, I cannot even feel it."
So you might analyze yourself and see which side needs training.
Our training ground is not only meditation, but daily life: people who tend to be highly energetic in daily life often have to work on developing relaxation and calmness, so that they will have that quality available during their meditation. On the other hand, people who seem quite calm and relaxed during their activity might need to work on building up high energy, to be able to take this quality into meditation.
Those who have succeeded in developing both sides, "marrying" them inwardly, have built the foundations for inner absorption.
Of course another element is essential for absorption: you will never be absorbed in something you don’t love. The element of love, or devotion, is a prime element for concentration: whatever you love, it’s hard not to think about it, be it a person, an object, God, or whatever. Absorption happens naturally as soon as you love.
This is why Yogananda wrote so many chants, saying "chanting is half the battle"; this is why he wrote so many devotional poems filled with divine ardor; and this is also why he himself prayed with intensely fiery love: "My heart’s aflame, my soul’s afire!"
God bless you and your meditations.
May you become absorbed in the bliss within,