I also start with the bar at about the center of my kneecaps.
For me personally, that seems to give my back the most and my legs the least.
If I were to pull that same weight from the ground, I would have a good bit of momentum by the time the bar reached that point. From a dead rest, it’s (mostly) all back.
No less an authority than Charles Glass recommends his clients perform partials. While the article I read didn’t mention specifics regarding starting positions, he did praise some advantages of rack pulls for the bb’er, including keeping the waist smaller. That bottom third of the ROM is what thickens the midsection – especially the sides – for many lifters.
Not the best result if you’re a physique guy or gal.
And if you’re particularly prone to lower back or SI problems, starting with the bar higher is much more forgiving on the lumbar region.