I am seeing a pattern between MN118 and MN119.. That says something about kayagat sati..
If you closely compare MN119 with MN118… you will find a pattern…
You will see that a paragraphs from Anapansati is taken and then it is followed by saying , while doing that when you achieve a state of unification(ekodi), and get settled (samadhi) then your mindfulness is considered as immersed into body.
Whatever is the object of attention(breath, body posture, body activity) but be peripherally aware of whole body and feelings. thats sati. and when it gets settled its called kayagat sati.
To further elaborate, lets say you got settled while doing breath meditation then here anapansati gone kayagat. You may get immersed in body by many other way, walk, eat, observing dhatu, parts of body etc etc.
Kayagatha sathi mainly focus on body organs like hair,nails, teeth,skin, lungus, heart etc. 32 organs separating to heart,water,Air and Fire that related to Four main Material Factors called "maha bhutha".
Anapanasathi focus on inhale and exhale. You can read and understand the difference well using below two links
May Triple Gem Bless You!!!