1) Sutta translations
2) Single objectness areas
Take for example this translation and commentary by Woodward
Here beggars, a beggar having gotten himself off to the forest,or to the root of some tree,or to some empty hut,and having taken up his seat there sitting down,setting the body upright,legs bent-across-lapwise, recollecting he attends to the face, just so he recollects inspiration,just so he recollects expiration.
and Vimuttimagga:Parimukhaμ satiμ upaÂÂhapetv¤. Whatever the translators of this phrase finally agree on, this means in practice that the meditator is to make sure (remember,recollect, mind, be mindful) that the various muscles associated with (pari —around) the organs of the face (mukham) (especially around the eyes, at thecorners of the nose and mouth, and the set of the teeth) are as free from tension as possible.Woodward translates: "setting mindfulness in front of him" and interprets according to the hindu-yoga tradition "Between the eyebrows, where the Hindus place the brow-cakram."
This is also found in the cambodian kammanatha manual as one of the "breath points".To the yogin who attends to the incoming breath with mind that is cleansed of the nine lesser defilements the image arises with a pleasant feeling similar to that which is produced in the action of spinning cotton or silk cotton. Also, it is likened to the pleasant feeling produced by a breeze. Thus in breathing in and out, air touches the nose or the lip and causes the setting-up of air perception mindfulness. This does not depend on colour or form. This is called the image. If the yogin develops the image [sign] and increases it at the nose-tip, between the eyebrows, on the forehead or establishes it in several places, he feels as if his head were filled with air. Through increasing in this way his whole body is charged with bliss. This is called perfection.
So I tried focusing between the eyebrows and my breath, and I noticed that passaddhi (tranquility) set in much faster, and I will continue to experiment with and report back and I remember doing this several years ago and getting interesting results.
Try it out!