I have no experience with this meditation but from a canonical perspective we have this advice from Buddha to Rāhula his son.
"Rahula, {any form whatsoever that is past, future, or present; internal or external; blatant or subtle; common or sublime; far or near: every form is to be seen as it actually is with right discernment as: 'This is not mine. This is not my self. This is not what I am.' There are these five properties, Rahula. Which five? The earth property, the water property, the fire property, the wind property, & the space property.
"And what is the earth property? The earth property can be either internal or external. What is the internal earth property?}[3] Anything internal, within oneself, that's hard, solid, & sustained [by craving]: head hairs, body hairs, nails, teeth, skin, flesh, tendons, bones, bone marrow, kidneys, heart, liver, membranes, spleen, lungs, large intestines, small intestines, contents of the stomach, feces, or anything else internal, within oneself, that's hard, solid, and sustained: This is called the internal earth property. Now both the internal earth property & the external earth property are simply earth property. And that should be seen as it actually is present with right discernment: 'This is not mine, this is not me, this is not my self.' When one sees it thus as it actually is present with right discernment, one becomes disenchanted with the earth property and makes the earth property fade from the mind.
"And what is the water property? The water property may be either internal or external. What is the internal water property? Anything internal, belonging to oneself, that's water, watery, & sustained: bile, phlegm, pus, blood, sweat, fat, tears, oil, saliva, mucus, oil-of-the-joints, urine, or anything else internal, within oneself, that's water, watery, & sustained: This is called the internal water property. Now both the internal water property & the external water property are simply water property. And that should be seen as it actually is present with right discernment: 'This is not mine, this is not me, this is not my self.' When one sees it thus as it actually is present with right discernment, one becomes disenchanted with the water property and makes the water property fade from the mind.
"And what is the fire property? The fire property may be either internal or external. What is the internal fire property? Anything internal, belonging to oneself, that's fire, fiery, & sustained: that by which [the body] is warmed, aged, & consumed with fever; and that by which what is eaten, drunk, chewed, & savored gets properly digested; or anything else internal, within oneself, that's fire, fiery, & sustained: This is called the internal fire property. Now both the internal fire property & the external fire property are simply fire property. And that should be seen as it actually is present with right discernment: 'This is not mine, this is not me, this is not my self.' When one sees it thus as it actually is present with right discernment, one becomes disenchanted with the fire property and makes the fire property fade from the mind.
"And what is the wind property? The wind property may be either internal or external. What is the internal wind property? Anything internal, belonging to oneself, that's wind, windy, & sustained: up-going winds, down-going winds, winds in the stomach, winds in the intestines, winds that course through the body, in-and-out breathing, or anything else internal, within oneself, that's wind, windy, & sustained: This is called the internal wind property. Now both the internal wind property & the external wind property are simply wind property. And that should be seen as it actually is present with right discernment: 'This is not mine, this is not me, this is not my self.' When one sees it thus as it actually is present with right discernment, one becomes disenchanted with the wind property and makes the wind property fade from the mind.
"And what is the space property? The space property may be either internal or external. What is the internal space property? Anything internal, belonging to oneself, that's space, spatial, & sustained: the holes of the ears, the nostrils, the mouth, the [passage] whereby what is eaten, drunk, consumed, & tasted gets swallowed, and where it collects, and whereby it is excreted from below, or anything else internal, within oneself, that's space, spatial, & sustained: This is called the internal space property. Now both the internal space property & the external space property are simply space property. And that should be seen as it actually is present with right discernment: 'This is not mine, this is not me, this is not my self.' When one sees it thus as it actually is present with right discernment, one becomes disenchanted with the space property and makes the space property fade from the mind.