there is more before the breath you know
but anyway, your interpretation does have some validity although the standard interpretation is watching the breath as it is and simply knowing the breath as it is, as has already been pointed out Thanissaro teaches some control is useful, knowing or letting the body know (don't mean we tell it what todo but allow it to know what to do without our interferance which prevents its knowing and self reliance) what it needs is a more midde ground than the strictly watching itor controlling it interpretations.
we are constantly controlling the body through different means, we concoct a frigtaning, or arousing thought and the heart races (causing stress), lyedown in parculiar postures and then complain when our joints freeze up (over stressed) attending to the wrong thought (stress) do it to much and a breakdown may happen (stress to over stressed), allow thing to be as they are but watch where problems could arise and alter the method to negate the problem before it arises, or after it starts to arise, then control isn't used and knowing the body is fully brought about.
Since talking with the people at DhammaStudyGroup I have thought a lot about this idea of "control". And I found out that I do not understand it. What is control? As you said, there is always control. Every thought, every emotion has a controlling effect on our breath (not to mention the rest of the body functions).
A bit farther down the satipatthana suttas states:
2. The Postures of the Body
And further, monks, a monk knows, when he is going, "I am going"; he knows, when he is standing, "I am standing"; he knows, when he is sitting, "I am sitting";...
I do not expect that anybody teaches not to stand up - a controled action, unlike breath which can be both controled consciously as well as unconsciously. Standing, sitting, going, lying down are all activities that require conscious control and the instruction is identical to the one on long and short breath.
But when doing the kind of meditation I described above I observed something else. At first I had to focus on controlling my breath - to make it long. I focused on controling my breath, I focused on counting the seconds and focused on linking both. But after a while this became a pattern that didn't require focus - or rather: no effort. Like when we learn to drive the car we need to focus on stirring and remember to look into the mirrors and the traffic and all that, but after some practice it comes so effortless we barely are aware that we have driven from home to work: a pattern, a program has been established in our mind that does not require control any more. So it was during that sitting. At first I needed to focus, I needed effort, but after a while, ten minutes or so, the control required for keeping the breath long was effortless, happening on it's own. That was why I was able to divert my attention to investigate that new, interesting, full-body awareness that blinked in and out. So was I controling the breath or not?
What if for those yogis like Buddhaghosa getting themselves into a long breath pattern came as natural as for us driving our own car to work? What if one just needed to tell them "breath long breaths" and all they asked "for how long?". They might have known how to control their breath for so long it came just as natural as standing up or sitting.
I suspect that the point about "no control" is that one needs to have an established pattern, so one can detach from it and observe. Meaning: first step is to establish the required pattern, second step is to turn to "knowing".
Again further down the satipatthana sutta states:
III. The Contemplation of Consciousness
And how, monks, does a monk live contemplating consciousness in consciousness?
Herein, monks, a monk knows the consciousness with lust, as with lust; the consciousness without lust, as without lust; the consciousness with hate, as with hate; the consciousness without hate, as without hate; ...
But how can one know the consciousnes with lust when lust never arises? How can one investigate hate when hate never arises?
And again further down:
4. The Seven Factors of Enlightenment
And further, monks, a monk lives contemplating mental objects in the mental objects of the seven factors of enlightenment.
How, monks, does a monk live contemplating mental objects in the mental objects of the seven factors of enlightenment?
Herein, monks, when the enlightenment-factor of mindfulness is present, the monk knows, "The enlightenment-factor of mindfulness is in me," or when the enlightenment-factor of mindfulness is absent, he knows, "The enlightenment-factor of mindfulness is not in me";...
How can one know enlightenment-factor of mindfulness is present when it never is present? How can one know there is a long breath if there never is a long breath?