Sony FE 28-70mm Edge Softness Problems - Is this the answer?

Further to my previous post, on the soft / smeared edges on the 28-70mm zoom at 28mm. I may have found an answer. See these comparisons below.

So it may be the OSS. As you can see the edge is definitely softer with the OSS on, but what I wasn't expecting is that the centre is slightly sharper with the OSS on. In fact the whole image with OSS off looks a lot smoother across the frame, but the whole centre area of the image of the image with OSS on looks sharper. 

I also tried this with a slower shutter speed for OSS on. Same thing happened. 

Now I won't even pretend that I know how Sony lens OSS works, so if anyone has an idea on this I'd be glad to hear it. Also if anyone else has the lens and would like to see if they could replicate this, then please post what you get on Google+.

If this does provide an answer then the idea of just leaving OSS permanently switched on, which I usually do, may not be such a good idea. At least with these Sonys. There is also the point that over the years I have learned to be very stable when I press a camera shutter. Even without any kind of IS I've always been able to hold a camera steady at slow shutter speeds. Considering that any kind of IS has to be switched off when using a tripod, this may also be exaggerating what's happening.

Anyway, I'll go and do some real shooting to see if this is indeed a 'solution' or not. As I said any feedback on this would be appreciated.

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