could you provide more information about how you took the pictures? Aperture and method of focusing (af/mf and continuous af or single shot?)? The lens seems to be tack sharp, although in some pictures focus seems a bit misplaced to me (fore example in the first picture the focus is slightly before the eye).
You mentioned the availability of a fisheye lens. As there is already the SEL057FEC which converts the FE 28/2 into a fisheye lens, have you ever considered using this combination (assuming that a port is available)? I highly doubt that there will be a native (in the sense that it is not an adpater solution) any time soon as the SEL057FEC is available.