"If you did a Natural Turn in the Foxtrot half way down the floor the amounts of turn cannot be the same as one that is at the bottom end and entering side two."
That is not actualy the distinction that the book is making.
Instead, it gives in the chart the amount of turn for commencing the natural facing LOD, such that you would be backing LOD after step three, having made 1/2 turn up to that point. (This would likely be used after a three step following a feather)
Then immediatly under the chart, it explains how to commence facing DW, make 3/8 turn, and end up backing LOD after step 3. (This would likely be used after a three step following a feather finish)
This 3/8 turn version (of steps 1-3 only) is the version I was comparing to the reverse turn, and also the waltz natural and reverse turns which share same alignments. What the foxtrot figures reveal in their foot passing is that the 3rd step moves down LOD in each case. In waltz, the 3rd step must establish a new direction of down LOD, but since the step itself is a closing in waltz this isn't as obvious as it is in the passing footwork of foxtrot.
And when the third step is a passing one, it will end up going somewhat across the yet-underturned body. But since it is not on or across the track of the standing foot, that step is not in CBMP - despite it's being across the body.