Originally posted by MBT74 I don't own the DA40 but from my testing it seemed that the FA31 is worst, the FA43 was better and the DA 35 f2.4 and the DA55 were pretty good using the wider points. I can't remember how the FA77 went.
Just look at the photozone.de or lenstip.com resolution charts. Or the dxo lens test field maps (if they have them for your lens). They will give you a good picture of what to expect of contast and sharpness across the frame for your lenses.
If a lens is soft across the frame, it is kind of unreasonable to expect the camera AF to be uniformly sharp and effective. The camera AF can only work with what your lens gives it.