Manufacturers of good quality galvanised shackles all state that shackles loaded at 90 degrees will have a WLL reduction of 50% (and 75%) if loaded at 45 degrees. I have tested for this and it is correct.
Stainless shackles will be different as they have a low yield and deform easily. In testing at 90 degrees they deform, which I might term as failing (but they do not actually break) to such an extent they are unusable at tensions much less than 50% of quoted WLL.
Shackles are designed to work in a straight line pull.
