I just noticed that in Ven. Thanissaro's translation of DN22: "There is the case where a monk — having gone to the wilderness, to the shade of a tree, or to an empty building — sits down folding his legs crosswise, holding his body erect and setting mindfulness to the fore [lit: the front of the chest]".
I don't know the pali word used for "the fore", but according to the inserted note, it seems that we should probably set our mindfulness to the front of the chest? To me the chest part is more sensible during breathing and it's probably better than focusing on the nostril, which is too restricted and could cause blood fixation on that spot. But why none of the translations I've found so far actually translated "the fore" into "the front of the chest"?