@papajoe
I've just joined this forum and, as in the case of so many things in life, one sees that pipe smokers vary widely in their preferences and protocols.
What I experience: I smoke to the bottom of the bowl and along the way I tamp VERY lightly so as to not form a tightly compressed mass toward the end of my smoke. (I will often lightly scrape off the surface ash instead of tamping) As a result, my tobacco usually completely burns leaving a dottle composed of nothing but ash - again, ash that is not tightly compressed. As a consequence, I will occasionally, at the end of my smoke, draw a bit of ash (few grains) into my mouth - a sure sign that I have bottomed out.
This event is not an issue for me and, I would suggest that, if you find that the presence of ash that you experience signifies that you have completely burned your tobacco, that's a good thing, i.e., you are not left with a dottle that contains incompletely burned (wasted) tobacco that you end up discarding.
Your experience also suggests to me that you are packing your pipe properly, i.e., perhaps following the age-old rule of packing in thirds: first third with very light pressure, second with medium pressure, third with firm pressure (so-called baby bear, mama bear, papa bear rule). Among other things, the initial, light-pressure packing allows for a more even (and thorough) burn.
Monk