The ‘Classics’ spell out the internal method of these two jin quite clearly. For Ti Jin (Lifting Strength) “...if you want to go up, first go down...” This means we must sink the Qi into the feet as we apply Ti Jin. For An Jin (Sinking Strength - moving energy down into the Earth.) “...if you want to go down, first go up...” This means that with the Qi already in our feet we allow the Qi to rise upward to the crown (Baihui) as we apply An Jin.
This is a bit of a simplification in that there are often multiple energy flows, many times in contrary motion, that is, simultaneously moving in opposite directions, present in these and other types of Jin.