Only saw your posting now.Can you tell me which AF settings you are using for AF . There are so many possibilities ?
With adapted lenses, there are not that many possibilities: Only "wide" (camera selects Focus point, not that useful, because it cannot know what you want to have in focus!), and flexible Spot S, M and L. Plus face detection (unfortunately: NO eye- AF) All the other options only work with native lenses (FE). In a way this is a serious limitation for adapted lenses, which limits the AF to basically a EOS 5dII level. I find it specially limiting for Sony A lenses.
So in 98% of all cases I use flexible spot L, sometimes M. I try to move my focus point where I need it. This is possible via activation of focus point (central wheel button), then with the direction buttons of the wheel, or the two little wheels on the front and back (thumb wheel). With portraits, it is always a little bit luck to really get the eyes sharp. But it is doable
The Tamron 28-75 looks really good so far, except wide open where it simply doesn't seem to be able to render even close to the resolution of the A7rII. Here is a link- only to a full frame Jpeg of the A7rII at f6,7:https://photos.google.com/share/AF1...?key=YmtXVlB2eFRySWhIZ2t5TzRZMjhpMEFmX2tnRnZB In terms of "rendering", nothing special really, but at least the lens can render a lot of fine detail here. I found the Sony 28/f2 to be less sharp. The Tamron is very useable from 28mm to about 55mm, the last 20mm are still good, just not quite as tack sharp. Given the size, weight and price of the modern 24-70mm/f2,8 zooms, I don't see that I am willing to spend that kind of money for such a lens.