Calculating bent normals is just an extension of AO calculation where the direction of each sample is also averaged along with the occlusion amount.
The bent normals from substance painter seem correct. In any region that there is no AO, your normal won't be bent in any direction, therefore in tangent space it's pointing straight up along the surface normal. This is why you only see details in the ears.
I have no idea how Unity handles the bent normals but the usual way is to, instead of applying AO as a standard multiplier onto the lighting result (which gives this weird muddy look), use the dot product of the bent normal and the light instead. This is how we handle SSDO in CryENGINE for example.
I've only ever used a texture-based version of this technique once, however in this version the bent normals also contained information from the original tangent space normal map, and was used directly during lighting in place of the original.