Detachment in breathing meditation I read this answer, and it made me wonder something deeply; the answer seemed to imply strenuous or volitional attention was inferior to watching the mind for breath meditation, and that merely observing was more effective. I have heard such a statement many times elsewhere, that too much 'expecting' or 'grasping' inhibits concentration. 

If this is so, how does a practitioner loosen their grip on the mind? How does one observe the breath with detachment?
Hahaha! Excellent question! What if the body did the breathing for the mind?
The biorhythm attached to the breath has its own tempo, as does the heart, the viscera, etc. When you exercise, fatigue accrues when there are disharmonies in those biorhythms - you don't get tired from being at rest.
The premise is enveloping one biorhythm in another, centralising your potential constant energy output. In other words your breathing is a result of your actions, therefore taking the conscious energy input (the mind) is on the action and not the breath.
To help wrap your head around this here is a practical exercise:

Find a quiet place.
Plant your feet comfortably wide apart, parallel.
Knees and hips remain stationary.
Tighten the belly.
Hands in 'prayer' comfortably above your heart (doesn't need to be touching the chest).
Following the movement of your latissimus dorsi muscles compress one side of your spine as if you were attempting to make your shoulder and your hip meet.
Gently shift that compression to the other side, and then back and forth. This will lead to a rocking motion which imitates two accordions working in tandem.
For those who know how to open the throat doing so may result in being able to hear your breath while your diaphragm remains stationary...
If you you do not know how to open your throat, continue the exercise while you think of other people yawning.
Listen for the gasping sound and experiment with the amount of movement required keep yourself going.

I have called it Bi-valve breathing and the benefits of the technique would be more clearly useful for martial artists however there are many applications.
Cultivate in harmony