I haven't looked through an SLC specifically.
I do know that the SLC (like most binoculars) has a classic edge, with intentional field curvature. The field curvature is there to prevent the "rolling ball" (angular magnification distortion) effect some people get when they pan with a flat-field binocular.
Try turning the focus knob and looking at the edges. I'll bet you can get them sharp by adjusting the focus.
Field-flatteners are an eyepiece component used in binos like the Swaro EL and NL Pure, The Zeiss Victory SF, and the Leica Noctovid. Cheaper options with field flatteners are the Nikon Monarch HG, Opticron Aurora BGA VHD, Athlon Cronus.
Basically field-flatteners are what makes a bino produce an image that is sharp all the way edge to edge. There are trade-offs though. Some people get the rolling ball effect. The other trade off is that the image has less 3-D quality (hence "flat").
Lots of people actually prefer binos with the level of edge curvature you mentioned. It's a feature, not a bug. If you'd prefer something sharper at the edges I'd recommend taking a look at one of the models I mentioned (but probably not the Monarch HG. It gets marketed as flat-field, but it has curvature comparable to what you described in the SLC).